I regularly take binoculars on hikes (even some light climbing that includes using the hands) and I've tried several models. I remember how sadly I discovered that my Zeiss Conquest HD 8x42 (my first quality binoculas) were not going to serve my purposes, so I moved to lower size and weight (which usually involves objective diameter). So, faced with the 20 vs 25 vs 30-32 mm I have several considerations. This is my personal experience:
- Pouch/case on the belt. I use this very often. I can carry the case on the belt or else, even better for less clutter, carry it on the backpack "belt strap". For this, you need a combination of backpack-binocular case that allows this. For example, I have a 55 L Vaude backpack where the belt strap is just too thick, but both my 42 L and 24 L Vaude backpacks can carry my favourite case, the one that came with the 8x30 Nikon Monarch 7. So that's a thing to check and consider when it comes to portability. Carrying the binoculars like this, allow to keep the binocular strap away (you can carry it just in case, hidden inside the backpack), but I find it very fast and convenient to grab the binoculars from the case without the strap tangling.
- Binoculars attached to the backpack. I have started to use this method this year and can't be happier. I also go mainly to the Pyrenees, Spanish side. And this Summer I used this system successfully even on +3000 m high mountains that required some climbing. No issue, you can either tighten the straps so the binoculars don´t hang too loose, or else simply un-click them so they are not in the way.
You can check more details about it
here:
Then, when it comes to what optics I personally find are the best compromise; well, you just have to check the image above.
To me, 8x20 or 8x25 (especially those with double hinge) have many compromises. The view is more fiddly, partly due to the smaller exit pupil, partly due to the smaller size (that makes grabbing not as ideal; I have average middle size hands) and especially for one reason. When I'm hiking on the Pyrenees I'm on the move (many times going up) which means my heart rate is higher than when I'm in an observatory. So ease of view is crucial, and that's where small 20-25 mm double hinge designs simply don't do it for me (other's may disagree, of course). I've found that I can carry the 450 g Opticron Traveller ED 8x32 (or a similar Nikon Monarch 7 8x30 at 435 g) and simply not notice the binoculars are there at all, even if walking for 8 hours a day. But if I try this with a double hinge 8x20 or 8x25, the view is really compromised. I get a lot of shake, unstable view and vibration that finally ruin the view. Not to mention that the two binos I've mentioned have a huge +8º FOV, which will make finding a lammergeier in the sky way or an "isard" in the middle of the snow way easier, while most pocket binoculars have way narrower FOV. Do check on that.
So, my choice is a sub 450 g 8x32 with a minimum of 8º FOV carried whether on a case on the belt or else attached to the backpack as shown.
One last word about materials. You already know that hiking on the mountains can put a pari of binoculars through a really strenuous test: but think about how possible it is for them to get scratched against a rock (they will) or banged agains the floor while you're doing something else. So my recommendation would be to go for ones with a rubber armour that covers the maximum amount of area.
Sorry, I feel I didn't answer your question. I had the Swarovski 8x30 CL Companion and rate them highly. Maybe they're a little too tall for the format, but they're a great compact. I found they had a little too much chromatic aberration for the price, but the view has really nice, with a lot of "pop", the view was rich and full of contrast. For me the deal breaker were the eyecups, too narrow for me (I struggle with narrow eyecups; again, ease of view/comfort is paramount). However, light and small as they are, I think I'll look for something a bit lighter and more compact (Nikon M7 or MHG, Opticron Traveller, Kite Lynx, etc.).
I have not tried the 8x25 Pocket (I had the 8x20 and, although the image were great, I wouldn't want to carry them as my only device for a trip where I might spot some relevant birds; too compromised). If possible, do try single and double hinge designs and see how they work for you.
