If you're looking to buy a new rifle, best try several first.
.177 for target shooting over distances is easiest, as the trajectory is flatter but it's also more affected by wind. Personally I find 0.20 the best all rounder IF you can find one!
Are you after PCP only? So no recoil? Or are you also considering springers or gasrams?
PCP's are easiest but the springers are more fun!
I've had a few rifles, the BSA Ultra multishot I didn't like, as the cocking mechanism is a bit fiddly and more steps than most other rifles. The AA S510 I really liked, very nice indeed but as I hunted I prefered the Weihrauch HW100 FSB 14 shot, which is excellent.
The rifle's only as good as the shooter and often personal preference over weight, balance and feel make a big difference.
So advice is try a few, at a club, mates rifles or at the shop if they have a range.