That's a very hard call. My H&K 51 has a .22 conversion kit that totally bad ass. Then again the suppressed Ruger MK II & 77/22 have been getting a lot of use.
Anything in .22LR, let's see in my safe currently sits a Walther P22, Ruger 22/45, and Remington Model 514 single shot bolt action. All fun in their own different ways.
Two Buckmarks and a 10/22 get the most play time at the range. Followed closely by the PT1911; it's just so much fun to shoot. Hi-Point carbine is quickly becoming a favorite as well.
My first gun was a Marlin 81TS bolt-action .22s/l/lr with a tube magazine. I've put tens of thousands of rounds through it and it's still as accurate as the day I bought it. The blueing is just starting to look worn in and it now has an old Weaver scope sitting on top of it.