The 442/642 is the 1 7/8ths 38 spl
The 638 is a 4" k frame aluminum
the 340 is the 357 with shrouded hammer
the 360 is the 357 with hammer
the 329pd is the titanium n-frame 44 mag (my next purchase)
then there's the 327 night gaurd, .357 8 shot
Those are the only ones I know off the top of my head.
Some of this is incorrect. There seems to be a lot of confusion about different J frame models. I don't know if there is a good guide to different S&W models on NES so I'm just going to write out some details.
First, don't buy a used Taurus. I will only speak to the revolvers since that is the scope of discussion, but their quality is much improved over past years - so buy new, not used. Second, just don't buy a Taurus at all.
S&W/Ruger > Taurus > Rossi/Charter > Joe Biden
Generally speaking, stick to S&W or Ruger. The Kimber revolvers are nice but don't seem to be what you're looking for.
Ruger
Ruger revolvers generally are overbuilt and therefore heavy, the exception being the LCR (lightweight compact revolver), which you can buy in 2" and 3" configurations, as well as exposed (LCR-X models) or concealed hammer (standard). LCR is known for a pretty nice out of box trigger. There are only a few grip options compared to S&Ws, though. The LCR comes in .22LR (8rd), .22WMR (6rd), .327 Magnum, .38Spl+P, .357 Magnum, and 9mm. The LCR notably has a replaceable front ramp sight, whereas most of the standard S&W J frame snubs have fixed front ramps. It should also be noted that any LCR front sight will also fit a S&W pinned front sight, though there can be some overhang on certain models if you are using a TruGlo fiber optic/tritium combo such as the TFX. If you want to use a tritium front sight, the best bet is the XS Standard Dot, which will need to be drilled for its pin using a #54 bit.
S&W
Now it's time to learn the S&W numbering system as well as the three main frame material types and three hammer types. We're only covering J frames here, currently the smallest frame size since the I-frame was discontinued.
For the hammer types, you've got the exposed hammer (double/single action), shrouded hammer (partially shrouded; can still be used in single action), and concealed hammer (DAO). These have been known traditionally as the Chief's Special, Bodyguard, and Centennial, respectively. One exception is that there is a polymer-framed, concealed hammer .38Spl+P model known as the Bodyguard with an integral laser and a very different cylinder latch mechanism. Otherwise, Bodyguard refers to the shrouded hammer models 38, 39, 438, 439, 638, and 649.
Material types -
You have the J frame models with 2-digits - these are typically steel frames, barrels and cylinders and I'm not going to cover them since you really just need to remove the first digit of a 3-digit model to get the model in this range. These are the heavy ones, so not what you seem to be asking about.
"Airweight" models are typically aluminum frames with steel barrels and cylinders (a mix of carbon and stainless depending on the model). These are probably the most common and are pretty lightweight revolvers suited for just about anyone.
"Airlite" models are the extremely lightweight revolvers. Scandium frames, and even some aluminum cylinders and barrel shrouds for the rimfire models (e.g. 317, 43C, 351PD, 351C). Also the titanium range is here. These things are exceptionally light. The first time you pick one up, you will feel confused that your hand is holding something your brain says should weigh more. These will go unnoticed entirely when carrying.
Now the numbers...
Prefixes:
3## - AirLite, may be appended with a TI for titanium. Finishes vary.
4## - Matte black Airweight
6## - Matte silver/grey Airweight
No prefix - typically a steel frame which may be blued or stainless depending on the model and year
The following may or may not have a prefix (in other words, a two digit only model)
#37, #31, 36, 60, 317 - Exposed hammer
#38, #49 - Shrouded hammer
#32, #40, #42, "C" models (351C, 43C) - Concealed hammer
There are some oddballs and exceptions like the polymer Bodyguard. I've purposefully left out a few oddball numbers. The 317 is a kit gun on a J frame unlike the Model 17 or 617 which are built on K frames, for example. I'm not going to go in to the exceptions too much here, but some of the titanium models and atypical J frame calibers apply: the 431 and 432 come in .32 H&R Magnum and are 6-shot models; the 940 is a 9mm steel framed Centennial, etc. Going sub-38 will net you more shots, like with the 32s (6rd, 431 and 432), the .22WMRs (7 rd, one more than the LCR, models 351 PD w/ exposed hammer and 351C), and .22LR (8rd, 317 and 43C).
Performance Center guns have been tweaked and may come with better sights, different grips, a better trigger, nonstandard finishes, etc.
To make a buying decision, first decide how regularly you are willing/able to shoot this gun. J frames have heavy triggers and shitty sights. Some models have better sights, some have great sights, and triggers can be immensely improved for smoothness and (within reason) lightness. However, any way you slice it, a J frame is a "bell curve" gun. They are not suited for average shooters, but they work pretty well for people who carry but don't shoot and people who can become an expert with the trigger and sights.
If you want an extremely light gun with magnum power, go with the 340 or 360 and recognize that they absolutely suck to shoot. You will not want to practice with them and any .357 ammo whatsoever. If you do, put a bandaid around the first joint of your index finger when you go to the range; it will help. Secondly, consider just carrying some decent .38Sp+P or even some plain old .38 wadcutters, which are actually a superb choice despite what anyone else will tell you. They will make shooting these guns very palatable. Also recognize that it is actually much harder to hold an extremely light gun correctly and on target while you are squeezing a heavy trigger than holding a gun with some (any!) weight to it.
If you want to stay light weight but don't care about .357, try to find something like a 337 TI. Some folks don't want to carry an exposed hammer because they think it will snag - they are wrong unless we're talking pocket carry, in which case just practice drawing with your thumb on the hammer. It'll never snag (but don't plan on using single action). You can also use hammer from a shrouded gun on an exposed hammer frame and it'll have less of a footprint. Some of the guns come like that, such as my 2" 317 which I think only weighs 11oz.
Some of the guns in the AirLite series have pinned ramp front sights (or come with tritium or fiber optic sights)...I like these because they are replaceable.
If weight is not the primary focus, pick your color and hammer type and choose a 642, 442, 638, 438 (harder to find; discontinued), or 437/637 and be done with it. These are the most common and least expensive J frames. They do all have fixed ramp sights, though. However,
Get yourself an Apex Tactical spring and firing pin kit - they cost relatively nothing, are easy to install, and will make for a lighter but reliable trigger pull. Then do 1000 dry fires and you're set. Don't screw around with your sideplate or frame screws without learning about them first and using the appropriate tools.
I won't talk about holsters but for speedloaders, don't buy an HK, they suck. The Safariland Comp I is infinitely better. SpeedBeez makes nice loaders but rounds can fall out if you don't carry these in their Kydex holder and unlike the Comp it's easy to send the rounds flying...SpeedBeez is best for the range. 5 Star is a better HK and stick with it if you must have a twist action.
Here's a pic of my 317 since I mentioned it. This is a 2" model, harder to find but much better made than the more recent 3" kit guns. Wearing Altamont grips. This one has a custom front sight dovetailed into the barrel rib by Dave Santurri, who also did the same for my 438. We used S&W Bodyguard .380 Truglo front sights and he did it for a very reasonable price. I carry this with Federal Punch .22LR, sometimes preferring my 43C or 351C for no reason at all, but a thread on why you should opt for a .22 snub over other guns is a thread for another day...
Anyway, hope this helps someone who needs to better understand the J frame landscape in the future.