JimPz
Depending on your preference, I would base it on cost, ergonomics & on a complete/existing bike, what is already on it & the cost/benefit to change.
+1
The only advantage I can see for a 10 speed setup is the potential to have smaller jumps in gearing between cogs. Having evolved from a 2X5, to an 3x8, and finally a 3x9; I don't really feel the need to "tighten up" the jumps between gears. I run a 44/32/22 crankset which keeps the ratios closer than a crankset with larger tooth differences between chainrings. Every once in a while I can't seem to find that sweet spot, but it is not often enough to make me think about gearing changes.