Muni is the uni equivalent of MTB, so that embraces a wide range of riding styles:
XC
Muni
DH
Wheel size is a different measure for unis than mtb, we do a lot more slow moving technical riding, so our standard width tire is wider for doing the same trails.
Maybe consider the terrain as a measure for what you ride, so rating mtb trails:
Begginer (green)
Intermediate (blue)
Advanced (black)
Expert (double black)
Extreme (triple XXX, fall and you get hurt)
Also consider which way you will plan to ride a trail, so to ride up an advanced mtb trail, you may need a lower gear and hopping skills, in which case a smaller wheel is better unless you don’t mind hiking (more).
You can ride technical terrain on any wheel size, so don’t let anyone tell you differently, it’s more a question of how well you can ride it, how much you’ll need to walk, etc…
Certain wheel sizes have an inherent advantage in certain terrain or with certain riding styles. For example, if you expect to do a lot of hopping, a 24" is going to be easier to hop than a 29". This doesn’t mean you can’t hop a 29" wheel.
In choosing a wheel size, it helps to know what you want to ride, but this can be a problem if you are planning ahead based on future skills development.
When I started riding muni, I planned to ride a uni on the same terrain that I previously rode mtb, so a mix of flowing single track to moderate technical terrain (roots, rocks, mud, drops 1-2’). I didn’t ride extremem mtb downhill, so I don’t expect to do so on a muni.
The biggest advantages of a large wheel are higher speeds and better terrain bridging. In places where a 24" has to be hopped, a 29er can often roll that same terrain. The downside of a bigger wheel is taller gearing, higher COG, and being generally more difficult to manage in extreme terrain.