There's a lot of good information if you want a 35. Recently I was sent one of the last new finger groove 177 Hw35s to tune. After working on it and shooting it I don't see the attraction to them. I know there's a whole crowd of people who love their 35s so my opinions may not be appreciated by them. I will post my opinions only to provide a pragmatic counterpoint for those considering either of these rifles.
I have a 177 Hw50 had and sold a nice 22 Hw50. I only sold it because I didn't like the caliber at that power level. After owning two Hw50s, working on a few others and working on and shooting a Hw35, I can say I much prefer the Hw50. Here's some stats and reasons why I prefer the Hw50s.
Keep in mind that they both make the same power.
The Hw35 is a full two pounds heavier with the same sighting systems. That's actual scale weight. Not advertised weight. That's a lot of extra weight for the same power. That extra weight will fatigue the shooter sooner.
The Hw50 is a little shorter. This and the lighter weight makes it a little quicker and easier to handle. Especially for hunting.
The Hw50 is much easier to work on. While some see the threaded block as a plus, it's a pain to work with. Also the threads can wear out. Granted it takes alot of disassembly/assembly to happen. Damage can be done to the threads if over tightened. Once the threads are damaged or worn there's no real fix for that that I know, other than replacing the compression tube.
The spring loaded barrel locking bar makes getting the barrel in place is a little trickier on the 35 as well. If you don't work on your guns none of these maintenance issues are a concern. If you do realize that it will take twice as long to strip and rebuild the 35.
I find the barrel release on the 35 more awkward and slower than a traditional break barrel. There's nothing magical about the locking system. It's still spring loaded opposing angles that are subject to wear. The only differences is you have to release it manually and it's not centrally mounted in breech.
The only plus I can find for the 35 is that it's longer barrel makes it easier cock than the 50.
Those are the physical and mechanical reasons I prefer the 50 to 35. Now for my personal reasons.
I much prefer the more traditional rifle looks of the 50. I don't like any of the abbreviated Weihrauch stocks. I find exposed breeches ugly.
The size, weight and stock design just make the 50 fit my style of shooting better. I find the 50 points and shoulders better than any other Weihrauch I've used. It's why it's my squirrel woods gun.
I've alway said my favorite rifles bar none are my Hw30s. I've also always said if I could only have one air rifle it would be my 177 Hw50. For me the Hw50 is the perfect balance of size weight, power and serviceability. Again these are my personal findings and if you prefer the Hw35 better because it fits your needs better. God bless you. Both guns are well made so there's no right or wrong here. It's just personal preference based on what fits you personal needs and tastes.
Be well
Ron