Whatever shoots the most accurately in your rifle!
CCI is usually a good bet, but buy a bunch of different stuff, whatever you can get your hands on. 22s can be very picky about ammo, it can make a big difference. I've read it and experienced it personally. Trying different ammo is basically like a reloader working up a load. Gotta get a good rest, put some paper out, try it and see what it likes. Sometimes you get lucky and the gun likes cheap stuff, and sometimes you don't! ;D
My Six likes CCI Mini Mags in LR and Winchester 40gr HP in Magnum.
I have a Marlin Semi that I still haven't found ammo for that it really likes, and they are known for being pretty accurate...