Which is inherently more accurate HW97 or HW50?
I owned an HW77K for a while. The 97K and 77K are the same action, spring, stroke length, etc. So the 77k that I owned is very close to the question you're asking. I still own an HW50s. When I had the 77k I was using it for field target, and put more than 12,000 pellets through it. The total running count on the 50s is closer to 15k.
The 97/77 is a bigger and heavier gun than the 50. Accuracy from springers is much more of a skill than getting accuracy from PCPs, and usually guys wanting supreme accuracy from a springer (talking field target here) gravitate to heavy guns. Mostly because heavy springers are a bit more forgiving of poor input from the shooter than light springers.
They can both be equally accurate, but it's usually easier to get that accuracy out of the heavier 77/97. Now, the flip side of that is that the 77/97 is a gun I wouldnt want to haul through the woods on a squirrel hunt. The 50 is much better suited to that. So "best" for you is going to be determined by use case. If you're wanting target shooting accurate, from a bench or for field target, I'd recommend the 77/97. If you're wanting a general use springer that's a perfect size for carrying around, I'd recommend the HW50s.
I played the springer game for about 4 years, and cycled through most of the high end options, searching for the best target springer. I ultimately sold all the heavy and big target springers, forsook using a springer for target work, and kept the svelte HW50s as an all-around "best" for my intended uses, mid-power springer.
The 50s just reminds me of light Marlin bolt action rimfires. Just the right size for carrying around.
A couple more thoughts....
The 97/77 is more of a 12-14 foot pound gun, and the 50s is more like a 9-11fpe gun.
The stroke length of the 50s is shorter than that of the 77/97, making for a quicker feeling shot cycle.
Been a long time since I put much time into springers, but if I remember correctly, current production of both the 77/97 and the 50 use a 26mm piston seal, just that the 50s stroke is shorter, hence the slightly reduced energy output.
Some say the fixed barrel, under lever springers are inherently more accurate than break barrels. Very few springer shooters in field target these days, and the few that there are, don't shoot break barrels. Springers are so damned hard to shoot CONSISTENTLY, that whether or not it's a break-barrel or under lever is WAY downstream of the plain and simple hard-to-shoot nature of the things. At least for me.
Can't put too long of a scope on a HW50s cuz it blocks the breech block from tipping up during cocking.
Don't want to put too low of a scope bell on an HW97 cuz it makes loading a pain, trying to finagle the pellet under the scope bell to get it into the barrel.