I have the full size and I really like it. People talk about the fullsize because it's made by Umarex... but it's got an aluminum slide, not Zamak potmetal.
I went with the full size because it shares holsters and ergonomics with my M&P 9. They're identical in size, so everything is a smooth transition.
My M&P 22 is the only I currently own or have ever owned that has never had a single failure and I am approaching 3,000 rounds through it now and that is about 90% bulk ammo from Winchester, Remington, and Federal. I've been very surprised by the gun. It's a great shooter. I did remove the safety levers so it matched my M&P 9.
I do want to get the compact, but really that's largely just because I like the full size so much.
I'm sure either of them will serve you just fine. If you don't need/want compatibility with the larger caliber brothers, then the compact is probaby a good choice, too.