When deciding on a variety to use for topiary you have to remember that the height that the plant will grow naturally will determine how tall your topiary will be. Sometimes people want a tall topiary and the variety isn't ever going to grow taller than 12" and they are disappointed.
I like to use scenteds for topiary. You can choose from various leaf sizes and textures that really make for a nicely proportioned plant.
Any pelargonium that doesn't grow as a rosette can be used. It's a matter of personal preference.
Debbie

May, I remember my MIL had a common geranium..this was back in the 80's and I don't know where she got it or what yr..Anyway, it looked like the common geranium, sitting in an unheated hallway, w/only a small east window.
Anyway, this geranium, grew long..It wasn't the scnted..It grew over 25' long, only one stem mind u, while the other leaves grew upward..The trunk was thicker than my wrist..She has this beauty for yrs, and then came up w/the idea to move to her hot, stuffy, dry LR..it then got mealy, and died that winter..
So, do you think I should order a scented? Is there any particular type? Thanks, Toni