My preference would be IQOPTION.COM
It is very quick and easy to use, plus I can use a MasterCard Debit card for deposits and withdrawals within seconds.
I dislike having to purchase Bitcoin first and then use them to buy the actual coin I want. This is long-winded, complicated and I have lost coins due to not being able to easily work out what to do.
I believe crypto has a massive future and the easier an ICO/Coin is to access the greater and quicker the uptake will be.