Not a fan of the high caps, as I find they exclude the vast majority of player-seasons in baseball history. Above $150M, you really need to be drafting career-best seasons from inner circle Hall of Famers in order to be competitive, and I find that's a very small pool of options.
I generally don't play anything over $100M, although I'll sometimes play seasons at $110M or $120M if I'm really intrigued by the theme. (Usually helps if the theme dictates a very restrictive and differentiated player pool for each team so that you don't keep seeing the same studs over and over.)
I'd say my favorite caps tend be between $80M and $100M because to me they afford the maximum amount of flexibility in terms of strategy. A $90M cap can accommodate a $15M pitcher or an $9M hitter without either becoming a giant albatross, but at the same time, there are a ton of players in the $3M to $5M range that are highly competitive at this cap. Most of those guys get completely outclassed above $120M.
That said, I do play in a $70M cap league that I really like, because it forces you to make some really uncomfortable roster choices. A $70M team is guaranteed to have some flaws, so you just have to decide which ones you're willing to accept.
I've never played a cap below $70M, mostly because it feels to me like it would be hard to draft enough innings or at bats to keep fatigue from becoming a huge factor. I know some leagues address this by letting you have AAA players, but I really don't like AAA, so that's usually a non-starter for me.