ST is more refined, quicker and seem to be less prone to rot etc than the ZS. But will cost more to run.

ZS, cheaper to run, feel more like a go kart and you could look to chuck a 1.7 puma lump in with little hassle or expense if you dont buy one that has already been done.

Puma's will prive hard to find without rotten arches and are a bit girly imo.

I would be tempted to try and pick up a zs with the puma conversion, would be great fun.