Will be some repeated information here.
#1. Discovery. For $600, could buy two and mount scopes on both. Would be a good introduction to PCP's.
#2. Sumatra (rifle or carbine). Gas hogs and loud, but from the box will earn between 50 and 60 foot pounds in .22 or .25. Are great hunting guns, less fun (becasue of air use) as a plinker/bench gun.
#3. Maraurder. Have had some problems guns, but they're working on that. Get one that works, and it could do it all.
#4. AirForce Talon/ Talon SS. NOTHING is more adaptable to calibers, barrel lengths, power output. If you like the military look and want to try different barrels, would be a great choice.
#5. AA s200. Simple, light, but lower powered. Accuracy takes 2nd place to nothing. If accuracy is your main concern and can live with 17-18 foot pounds (in .22), this is your rifle.