I’m just about to build up a second Scandal 29er, one will be a rigid singlespeed and one will be geared with bouncy forks.
One frame is slightly larger than the other, so I’m pondering which way around to build them. (I’ve run the smaller of the two as both a geared and a SS bike and liked it both ways).

Any opinions on which way around would work best?

I always find climbing out the saddle easier on a longer bike. So maybe the bigger one might work better as an SS since I imagine you’ll be doing most of the climbing out of the saddle!

Good point, so +1 to the larger bike as a SS up hills.
Downhill I was thinking that I could run a shorter stem on the larger bike so better as a “play” bike – also better for the SS maybe?