Glad this thread got revived, there are some real nice .22s here!
I'm a fan of the Colt/Walther M4 .22lr and got one a couple years ago. It still shoots great after thousands rounds and is reliable using Federal value pack (glad I stocked up over the last two years!) Accuracy is good, about 1.5" at 50 yards. I looked at the S&W M&P15-22 and liked it but the Colt felt better in my hands, the metal receivers bring the weight up to about the same as the M4/Colt LE6920.
Mine is the first generation with the dumb 180 degree selector and dust cover that flops open. The new ones have the standard 90 degree selector and I'm thinking of adding the new part. Anyway, the S&W is a great choice but pick up the Colt and compare, you may like it better. BTW, there's a lot of negatives out there on the net but take it with a grain of salt. People who actually shoot them tend to like them.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek