I'm in exactly the same dilemma.
I've got a 4-16 S&B P4f, which is a really nice scope, but I want a bit more magnification.
I'm also looking at going the H59 route. Although I really think the TReMoR2 would be great for Practical Long Range shooting (once calibrated correctly), but it's useless for me as I can't use the same scope for practice with my long range 'air'-rifle on my small holding as the TReMoR2 WindDot curves are completely wrong (seems it won't work for .22lr and below).
So next came the question of 3-20 or 5-25... here's my research so far:
I'm wanting to shoot Practical Long Range competition with my AIAW .260 (200m zero), and that means targets between 200m and 1000m, which is pretty much a perfect range split for my .260, so I then took a look at the magnification that I would need in order to engage a target at 1000m with a full cross wind. i.e. using the full width (wind) of the H59 reticle when targets are at 1000m (unlikely case @ 42.8Kmh/26.5mph). In my case this is at -9.5Mil which is the bottom row of the H59 pyramid (actually -9.1Mil, but you need to see the next row to estimate the offset.
The tunnelling on the S&B's seems to follow the FOV, so min FOV needs to be considered at where the tunnelling starts. On the 3-20 it's estimated at 4x and on the 5-25 it's estimated at 7.5x, so FOV range can really only be interpolated from there upwards.
On the 3-20 that means that I need 19.5x magnification to see the full H59 reticle width (at -9.5Mil), or 20.14x to see just the -9.5Mil vertical in zero wind. So the 20x should be fine for the application of view that I want to use this scope with, as I'll always be able to see the full reticle that I need. A max zoom of 20x, I'll be able to see the full 8Mil (930m) wind range.
On the 5-25 it requires 20.85x magnification to see the H59 full reticle (at -9.5Mil), or 22.7x to see just the -9.5Mil in zero wind. At maximum magnification of 25x, I'll be able to see the -7.5Mil (900m) at the bottom of the reticle and have the full usage of the wind stadia at 5.5Mil (750m). So if you zoom past 22.7x magnification, I'm going to lose the bottom of the reticle that I need to engage targets at that distance... which sort of negates some of the point of the high magnification when I need it... although what is the percentage of targets between 850m and 1000m in competition. I almost wish that the H59 was offset 5Mil vertically similar to the H37, which would then make the 5-25 perfect. I guess I could always dial 5 mil when past 800m... which I was wanting to avoid with the H59 in the first place... or just zoom out to 21x.
*Note: the above have been 'calculated', so there might be a bit of variance compared to the real scope. (but I doubt much)
I'm not sure that I'll need the 3x rapid target acquisition with a bolt-gun, and my 4-16 has never given me any worries about not finding targets quickly... so 5x would probably also be ok. (I tried leaving my current scope at 5x for a while and really didn't notice much difference in acquisition.)
The 3-20 is 920g and the 5-25 is 1080g, and the 2-20 is 385mm long vs the 410 of the 5-25. Not a huge amount in it, but every little bit adds up I guess if you're lugging it around all day.
So not a lot in it... and it's going to come down to the application that you want to use the scope for.