Sure folks have debated the merits of each exchange ad nausea but wanted to approach the topic on some of the key considerations. If you think an exchange is "Best" based on the criteria below, feel free to reply down below.
1. security/fund safety/etc: priority number one is safety of the funds...this excludes a number of exchanges such as bitfin where customer funds were hacked and not fully reimbursed; any new exchanges recently popped up with less than 3 months or preferably 12 months of operational history are suspect too, unless they are backed quasi-govt/fortune 500/insurance/bank etc
2. mobility: any exchanges such as some in Japan where only local residents can register does not fit this criteria. The exchange could be incorporated in singapore for example and operated out of japan, does not matter as long as they are open to residents of most countries without undue restrictions/KYC burden
3. liquidity: this will depends on the token, but the exchange should have decent depth at least for the major tokens (btc, eth, ltc, xrp, etc)
4. flexibility to convert back to fiat: coinbase is a major one (good or bad depending on each user's experience)...but are there any other good crypto-to-fiat exchanges other than coinbase? crypto-to-crypto exchanges unfortunately would not fit work.
5. low commission: not uber important not nonetheless the withdrawal fees and commissions can add up quickly for high volume traders
Just never never never use CEX.io
