I think it really depends on what you plan on doing with it and how much your willing to spend.. I am pesting, so i wanted something compact, powerful, and quick follow up shots. Secondary concerns were noise level and cost. I went with the .25 wildcat and it has blown away my expectations as a first PCP for me.
Are you shooting paper at 100yards or squirrels? Are you shooting from a bench or off hand? Do you plan to shoot a dozen pellets per session, or several hundred? Where do you live?
There addicting I just got My first one a HW100 and now I find Myself wanting more!! It is hands down the most accurate enjoyable to shoot gun I have ever owned.
A gun that has the power to push a heavy pellet (heavy .25 or .30) at least 860 fps (or so) would be a good start. Any top brand high end gun will be pretty accurate. The rest, as others have said, depends on what your particularly want to do with it.
I've got a bsa r10 mk2 .22. It's a shooter, haven't got it out past 50 yet but it's accurate. There'sany good options, bsa, evanix, fx, daystate, airarms, ect. Depends what best suits you, you wanting a regulated gun?