My best choice platform for day trading is Poloniex and second which I choose is C-cex. This platformed were fast and secured to use. Ive been trading this platform since last year so far I havent encountered any problem.
The best platfor to do is to trade with all trading sites so that you have more capabilities to trade. Since every exchanger has their difference prize per coin, it does mean that you can take all of them as advantage. As I trader, I give funds in several trading site and once I seen which trading site has a cheaper coin price, I do buy from that ste and I transfer that coin ti another site which has more expensive prize for that coin has a larger volume for their trade.