Both are nice rifles. I have a HW90, but not a HW97K -although I have shot them.
The HW97K is probably the better rifle, for most people, but I prefer gasrams.
I also mostly avoid underlever rifles as I don't like putting my fingers into a potential guillotine (the sliding breech).
If you only shoot out to 35yds, then a .22 would be adequate to shoot that far and will be a more reliable stopper if your shot is not quite perfect. Anyone who says that the odd stray shot doesn't happen, is either very good, very lucky, or just plain lying.
.22 will also have less harshness to shoot than a .177.
Of the two, I would choose the HW90.22.
Most forum members would suggest the HW97K.177.
HW100TK.177;Lightstream 4-14x44FFP. HW100TK.22:NVRS-F+doubler. Rapid mk1 .20:Lightstream 4-14x44FFP. SLR98.22:SR6NE 3-12x50IR.
Evo-T.177:SR6 3-12x44. Evo.25:SR6 3-12x44. TXHC.20:Falcon 4-14x44FFP. TXHC.25;WTC 1-5x20.