Really love my Ruger Mark IV 22/45 lite. 2nd choice would be my M&P 22 compact.
Both really great shooters but like said above, the skies the limit on upgrading the Mark series of ruger pistols
1. Usually excellent trigger out of the box and very accurate.
2. Will eat almost any type of ammo without jamming once it is broken in.
3. Much easier to clean IMO than Ruger Mark Series.
5. Easy to get replacement parts and aftermarket parts
6. Relatively Inexpensive.
I've had excellent luck and a LOT of fun with my Ruger SR22. Mine is the TB (threaded barrel) option, though I've never had a can on it. It's been utterly reliable with all kinds of ammo. And I've gotten some downright silly accuracy out of it, hitting 10" plates free-handed from 100 yards. But it's not something you'd really tweak or customize IMO. If I were to pick a fun base to start building on, it would be the Ruger Mark IV 22/45 Lite for me. My younger brother has a Mark III that he's upgraded with Volquartsen parts and it's an absolute HOOT of a gun.
In terms of a "platform", I think you'll have a hard time getting anything better than a Ruger MK series.
Not saying they're the best out of the box option, but just like the 10/22, you can do pretty much anything under the sun to a MK series.
My MKIII 22/45 Lite was on the chopping block, but some VQ goodies installed by INGO's own Turbo has made it a keeper. My newest favorite .22LR pistol is actually the cheapest - Ruger Wrangler. I have a Beretta 21A to test, and wouldn't mind snagging a GSG 1911 at some point, but in terms of an overall platform, I'd have to go with the Ruger. Haven't shot one, but the Browning Buckmark is high on the list as well.