I would say buy what you like to look at. It would suck to have a rack full of babies that are not selling that you hate to look at daily, when you clean all of those tubs.
I think the Tri Stripe would be my starting point if I was just getting into Balls. The Puzzle is not a bad morph to start off with either, depending on funds. If I was starting out today, I might pick a main morph, say the Tri Stripe, and build around it. Get some Pastel Het Tri Stripes, make some Tri Stripe colored morphs, and finally add it to some other pattern morphs.
I would say stay away from Spiders, the wobble, Caramels, the kinking, and Deserts....
Dave