I have been involved in full auto now for about 5 years. Right now I have an Uzi 9mm, MAC 10 .45, Ruger AC-556F and an M16. I love all of them. For a SMG I would go with the Uzi and if you want a rifle I would go with the Ruger AC556 if your on a budget. You can grab a Ruger for 5 to 6K if you look hard enough. An Uzi will run you around 6K or so also. The 16 will run you 10K or more depending on what you get. These are all approximations.
My opinion..... the Ruger AC-556 is a homerun. I have loved mine since day one and I will tell you that its still my absolute favorite. As long as you feed it with good factory Ruger magazines (not the aftermarket crap unless you know your stuff and what your gun will take) you will get some real good fun and pleasure out of it. Its a real robust, rugged and reliable weapon that is made by an excellent company that backs all their products.
Up until last month Ruger was working on the AC556 guns. They put out a statement last month and I spoke with a buddy up at Ruger in Newport, NH that says they are no longer working on the AC guns due to exhaustment of all parts of the weapon. Depending on the problem they may work on it but they are flat out of parts for the gun. Mine is a 1981 AC shorty folder and I sent it to Ruger a year ago for a tune up and they replaced a ton of parts and did not charge me a penny.
Either way you cant go wrong with an Uzi or the Ruger. The MAC is ok too because you can put all kinds of stuff on it like Lage slowfire conversions etc. but I prefer the Uzi over anything else. Also you can pretty much count on purchasing a .22 conversion kit for any of the full autos today as well. I have a .22 kit for my M16 and I love it. Cheap full auto fun. You can get one for the Uzi, Ruger or pretty much most MGs too if you want.
Here is my AC-556F and again.... its my favorite MG. Good luck in your search and if you ever need any help locating what you want or would like to try mine to see what suits your fancy let me know. Also check out "uzitalk.com, ar15.com" and of course the NFA section of this site.
http://img.photobucket.com/albums/v673/5150rob/001-2.jpg
one piece of advice.... dont ever start this MG hobby by saying.... I will only get just one and then I will be happy.... it will never happen.... you wont be able to stop. Its an addiction...
like a NFA buddy of mine always tells people.... "shooting semi auto is like having sex with your Wife or your Girlfriend.... shooting full auto is like having sex at the playboy mansion all night long."
I mean no disrespect by this comment... I just always thought it was kind of funny. hold on................... needed to make sure my Wife was not reading over my shoulder. Ha ha....
good luck and let me know if you need anything during your search.
Rob