I want to hear from you that own both 24" and 26" MUni’s. I don’t really want to know which is better, just which you actually ride the most. I won’t tell you which of mine I ride most and why until a little later:p
In my opinion, I would prefer the 26" muni even though it is slightly heavier and bulkier than the 24". I’ve been using 175mm cranks on my unis, and i find the on the 26, the pedals doesn’t bite into the dirt like the 24 does when i do sharp and steep turnings. Also when riding, i find that the 26 actually climbs better and feels smoother compared to the 24. The larger wheel diameter actually smooths out the bumps. 
The 24x3 gets the most use. I find it preferable for conquering roots, obstacles, etc.
My first Muni was the 26x2.6, I think my success rate went up when I got the 24. I used my 26 as a backup Muni when my 24 was in the shop a while back, it just doesn’t suck up stuff and bounce around as well as the 24.
I have both, I ride the 26 more then I ride the 24.
Whichever. I just think it’s good to have a distinct use for each unicycle in your fleet.
If I were to choose a brand new MUni, specifically for MUni, it would be a 24 with a fat tyre. That would give it a rolling diameter of approximately 26 inches!
If I were to choose a general purpose uni with some off road capability, I would choose (and in fact I own) a 24 with a 1.95 tyre with a few knobbles on it.
If I were to choose a unicycle for covering reasonable distances on rough ground, I would choose between:
A 26
A 28
A 29
A Coker.
In my actual fleet, the 26 with a Gazz 2.3 tyre, a Reeder handle and 150 mm cranks is the dedicated MUni.
As for the earlier comment about pedals digging in on turns: a smaller wheel requires shorter cranks to give the same mechanical advantage. 170s on a 24 sounds very specialised to me. I never could get on with 170s, even on my 26. I ride a Coker with 150s, 26 with 150s, and almost everything else with 110s or shorter. 28 with 110s is fun - and the pedals NEVER hit the ground in a tight turn.
my opinion
It’s interesting to hear your opinions. Thanks! I used to prefer my 24" muni with the 2.6" tire, lighter wheel and frame and 175mm cranks. It climbs great and lets me go down really steep hills with more control. Lately however, I find myself reaching more and more for the 26" muni with the 3" tire and 170mm cranks. I think it’s mostly because it just gets everywhere so much faster and I’m getting better at muscling it around. It rolls over stuff easier and is all around more comfortable. Better flotation from the tire width and diameter lets me get through soft stuff better. Mikefule, I don’t see how you can ride with such short cranks at all. I think that subject of crank-length preference is rather complex. One of my sons prefers much shorter cranks than the rest of us, and it doesn’t seem to harm his hill climbing abilities at all. I don’t get it 
Re: my opinion
First, be able to idle your normal uni indefinitely. Be able to freemount as near to 100% as makes no difference. Now is the time to try shorter cranks.
Short cranks do reduce your hill climbing and descending ability. There’s no doubt about that - it’s simple mathematics.However, on short cranks, you can achieve a lot with two approaches:
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The rush. The short cranks allow a higher speed, and you can rush up short slopes relying on momentum.
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Timing and balance. Riding with a low crank length:wheel radius ratio (short cranks and/or big wheel) is a cooperative venture with the unicycle. You can’t simply dominate it. So you read the road ahead, accelerating or slowing down 2 or 3 wheel turns earlier. You stand up on the pedals and tip toe through tricky sections, relying on the feed back through the soles of your feet. The bigger wheel has a slower natural rhythm, so you fit in with that, rather than trying to impose your own rhythm on it as you would on, say, a 20 with 125s.
It’s not for everyone, but it is fun. The other advantage is that when really challenging terrain is not available, shortening the cranks reintroduces the challenge. It’s like a terrain upgrade. 