I've owned/own a good many of each. Diana/RWS models I have owned include a RWS 52 .177, RWS 48 .22, RWS 46 .177, RWS 24 .177, RWS 35 .177, and a RWS 350 .22. I can't say they aren't good guns, they are. They are just not quite up to Webley & Scott or Hermann Weirauch quality, IMO. My favorite are the 48/52 side-levers and the RWS 35(about a 20yo gun!). Things that turn me off with Diana/RWS is the huge about of barrel droop involved with most of their guns and the absence of butt plates on several of their models. The RWS 48 is still the best deal out there if you're looking for the most ftlbs per dollar spent. You just can't beat it.
I've owned a few more Beeman/HWs. Those include Marskman 40 .177, HW-35 .177, HW-55sm .177, HW-55 Champ .177, R-7 .177/.20, R-9 .177/.20/.22, R-1 .177, .20, .22, .25, RX-2 .22, HW-77 .177, HW-97 .177/.20, R-6 .177, and a R-10 .177. Guess what, ALL of these have buttplates! :lol:
The R-9s and R-1s are simply a breeze to work on. I really enjoy taking them apart! Then there's the Rekord trigger that is standard on most Beemans. The finish on the HW/Beeman guns is certainly a step above the current Diana/RWS guns. The Beeman/HW dovetail is CERTAINLY better than the raised dovetail found on RWS guns. Also consider you have to take barrel droop into consideration when purchasing scope mounts for a RWS rifle, not so much of an issue on the HW guns. Also you have to consider asthetics. The RWS 34/45/40/36 series are out of proportion looking. All BARREL! I know the R-9 is only two inches shorter but it looks MUCH better!
The ONLY RWS Diana gun I recommend is the 48/52. I like it. It's short, compact, and packs quite a punch for the money spent. I use the Beeman 5032 one-piece mount with droop compensation built in.
To contrast, there isn't a single HW/Beeman gun I WOULDN'T recommend. Depending on ones pocketbook and needs, there's a Beeman/HW gun for practically every user.