As with a .22 RF rifle, you need to try available brands and grades to find out what your pistol likes best, and to shoot it from a solid rest to find that out. Lapua Midas+, RWS R50 and Eley match is where I would start with some of the less expensives added. Its a fun process. Get a box of whatever you choose and go to it.
I really think this is pretty bad advice.
I seriously doubt anyone could shoot the difference between these top line ammo, and less expensive offerings from these (and other) manufacturers.
I've ransom rest tested numerous high end target .22s, and while there can be a difference between (for example) CCI SV, and Tenex Pistol, it is usually trivial, only statistically significant, after many large samples of each. More importantly, any difference would not represent any score differences, on either NRA Bullseye targets, or ISSF targets.
Bottom line, almost all quality target .22s, can hold the 50yrd x ring with any decent ammo.
Many people shoot Master level or better scores with CCI-SV.
I especially would advise anyone to not attempt 'group testing' with a pistol like we do with rifles. The error introduced by the shooter will dwarf any differences in actual accuracy..
The important thing is absolute reliability.
Next is shooting enough to gain a level of competence. This takes lots of ammo (and more dry firing). Of course if you're not going to compete, then reliability is really the only issue, from an enjoyment standpoint. But then you certainly don't need expensive top end ammo for that.
I've competed in various handgun disciplines for more than 50 years, at many major regional matches, Camp Perry, etc. I never saw, or heard of, someone shooting Midas+. I have been at major matches where at least half the field was shooting CCI-SV.
I would encourage the OP to post this question on Rim fire Central, Targettalk, or Bullseye-I forums. Bullseye-I esp. focuses on handgun, Rim fire Central has a High Standard specific sub-forum (featuring long-time factory gunsmith and personnel).
I have shot at various times, a High Standard Supermatic Citation purchased in 1965, 2 Pardinis, a High end 1911 conversion, a couple of Rugers, and a Benelli.
I still have the High Standard, and one of the Pardinis. I shoot mostly CCI-SV, Eley Club, SK Magazine, Wolf Match.
Dave