Any suggestions on which of the pellet samplers would be a good choice to try? At the moment leaning towards a RWS 34 Rifle.

Depends on your gun. If it's a high powered "magnum" then I'd go with one that includes some heavier pellets.
To you other post, the just introduced "Assembled in the USA" Benjamin Trail NP2 ($250)is getting mixed reviews but getting better as they work the kinks out. My BIL has one in .22 and is very pleased. A little over your stated price range, the RWS's are a good choice. For just a bit more than the 34, Pyramid Air has the RWS 350 Feuerkraft Pro Compact on sale ($299).

http://www.pyramydair.com/s/m/Benjamin_Trail_NP2_Air_Rifle_Black/3367

http://www.pyramydair.com/s/m/Diana_RWS_350_Feuerkraft_Pro_Compact/1502

Another option, link here
I set up targets like these, link here and keep good notes of which works in MY rifle and which don't.
It's worth the effort, Good luck on the search!

Try as many different pellets as you can.
You may find some of the cheap ones outperform the high dollar versions

Also, it's good to know you can use several different kinds for different purposes

One one my guns really likes cheap Crosman flat points from Wally World, but will barely hit a 9 X 11 sheet of paper with their pointed style

You won't go wrong with a 34 in .22. I'd try some Crosman HP & Pointed, RWS Superdomes & H point. All of these shoot just fine in my 34 Panther.