I don't know what the best magwell for a 1911 is, but I'm using a cheap Wilson Combat "clip on" on two of my single stack 1911s (.45 ACP and 9mm) and a Smith and Alexander Magwell/Main spring housing on a wide body 1911. The S&A moved my P-16 out of ESP (IDPA) (weight) and into Limited or L10 in USPSA.
Remember to check the weight of your gun and magwell, also make sure you know if the gun needs to be modified for the magwell.
Respectfully,
jkelly