The topic of wheel size comparisons seems to be popular right now.
There are two factors to consider when comparing wheel sizes and tires. The first is tire width and the second is wheel diameter. The tire width affects how much cush and impact absorption the tire has. The diameter affects how fast and how maneuverable the wheel will be.
I have both a 24x3 muni and a 26x3 muni. Both have the 3" Gazz tire. I also used to have a Pashley with a 26x2.1 XC tire. I have ridden unicycles with a 26x2.6 Gazz Jr. tire. My 24x3 is a KH Pro with 170mm Profile cranks. My 26x3 is a DM Vortex with 175mm DM splined cranks.
The 24x3 and 26x3 are very similar in how they ride and what you can do with them. The differences are mostly in maneuverability and weight. There is a big difference between a 24x3 and a 26x2.1 XC wheel. There is a very noticeable difference between the 3" wide tires and the 2.6" wide tires and the 2.1" XC tires.
The 24x3 muni is my fun muni. The 26x3 muni is my cruiser muni. The 24x3 gets ridden a lot more than the 26x3 muni because I generally want to have as much fun as possible during a ride.
The main difference between the 26x3 Gazz and the 24x3 Gazz is a slightly different tread pattern on the tire. The 26x3 Gazz has a tread pattern that doesn’t like to turn as much as the 24x3. Combined with the larger diameter of the 26x3 it is more unwieldy to ride when trying to make a sharp turn for something like a switchback or a sharp maneuver to avoid a rock or other obstacle. I need to try a different tire on my 26x3 to try to find a 3" tire that is more maneuverable on the trail.
The other difference between the 24x3 and the 26x3 is that with the 24x3 your pedals are in the stable horizontal position more often. That means that you can make more corrections while riding. That helps to make the 24x3 more manageable especially in terrain where you are trying to maneuver around rocks and roots and doing little hops.
In general the 3" tires allow you to plow in to rocks and roots to get over them. The 2.6" tires don’t have as much give and don’t like to just plow in to rocks and roots. You have to have a little more finesse with the 2.6" tire to get it over rocks and roots. The 2.1" XC style tires don’t like to plow in to rocks and roots at all. You need a lot more finesse to get a 2.1" tire over roots and rocks. You have to do a lot more weaving and look for the smoother line. There is a big difference in riding style between the three tire widths.
The difference in riding feel between a 2.1" XC tire and a 2.6" Gazz Jr. is about as significant as the difference between a 2.6" Gazz Jr. and a 3" Gazz. Going from a 2.1" XC tire to a 2.6" tire is a big change. Going from a 2.6" tire to a 3" tire is a big change.
Your riding style will determine whether a 3", 2.6" or 2.1" tire will be most suitable for you, irregardless of wheel diameter. Trying to compare a 26x3 to a 29er just because they have a similar diameter is silly. You’ll know which one is the right size based on how you are going to ride it and where you are going to ride it.
I can ride my 26x3 everywhere I ride my 24x3. The 26x3 is harder to maneuver and harder to jump with, but it’s up to the task for anything I can do on my 24x3. I’ve ridden elevated skinny logs and done 4.5 foot drops with the 26x3. I would never ride an elevated skinny and do a 3+ foot drop with a 29er, the wheel would not survive for long.
The comparison between the 26x3 and the 29er gets more interesting when considering XC style riding conditions. With XC riding the trail generally has less rocks and roots and the objective is generally speed. For a buff trail the 29er would have the advantage. If the trail is more rocky and rooty then the 26x3 could possibly hold its own because it would be able to plow straight over and straight through the rocks and roots while the 29er would need to slow down and more carefully thread and weave their way through and over the rocks and roots. But a rocky and rooty trail like that is not your typical XC trail.
So tire width comes down to determining your primary riding style. 3" for more aggressive riding, 2.1" for very XC riding, and the 2.6" for something in between.
For roll over there is not much difference between the 24x3 and the 26x3. But there is a big difference in roll over ability between a 20" trials uni and a 24x3 muni. It is difficult to roll over things with the trials uni but easy to roll over the same things with a 24x3 muni.