Recently I've started my trading on Bitmex, so you know what? I completely don't like their charts, moreover I don't like when tick on ethereum is too big, like 5 cents. Don't repeat their mistakes
But these are somehow minor details. The most important aspect is the liquidity of the order books. It's not fun if you can't sell or buy at a reasonable spread.
Also there must be marginal trading and good security protect.