I'll add that the only thing that causes the same version of tractor to have a lower pto hp is if it's a Hydrostatic drive vs manual gear shift. For example my CK20s claimed 17.1hp at pto (gear) vs 16.2hp at the pto for the Hydrostatic drive. This is because the pto is driven off the transmission. There's pro's and cons to both transmission offerings. And as the tractors get bigger you get more manual transmission offerings potentially. Frankly even though I've got a manual likely for more users a hydrostatic drive is the best choice.
I would suggest consider the type of work you want to do, the implements needed, the power they will require and then size the tractor accordingly and get something that will have a bit of power to spare at the pto vs being maxed out to do the job. Same thing for manual vs hydrostatic, consider your tasks. Personally I'd suggest like I said above hydrostatic will likely be the best choice, certainly for a smaller tractor, in my mind I think I'd only really want manual if I was doing heavy field work and I'm sure there's users out there that will even argue that. Anyway, if you're doing odd jobs, loader work, really anything that involves back and forth vs just being at one speed for a extended periods hydrostatic is your friend.
The only reason I got a geared tractor was that it was cheap and I grew up with geared tractors so it's what I know. I can work the gears and not hurt my clutch doing loader work but I know ultimately hydrostatic would have been a better choice for what I do.
Bit long-winded but I hope that helps you a bit.
E.