I've used both types at a chiropractor office. The goal was to stay reasonably active while doing head weights. They both work to some extent. Seems to me the type with the solid top tip until the edge catches. But I liked the solid flat surface under my foot.
What do you want to do with them?
If you are into hardcore balancing, I'd make a rola bola and use that in a safe place. Rola bolas are a lot more dangerous but you look a lot cooler when you juggle chainsaws on top of one.