Are you looking for trading or for converting fiat to Crypto?
For trading the best at the moment seems to be poloniex (BTW I don't trade but as far as I know).
For converting Fiat to Crypto Bitstamp is cheap and reliable but you need to set up an account then transfer money, Coinbase is an alternative and is probably the easiest and quicker to get set up with. You can add fiat via bank card which is on your account instantly.
One last point, all of these options mean putting money on an exchange. That means your open to the possibility of losing your money if the exchange goes out of business. I would limit how much you transfer and when the exchange has been done move your balance off the exchange. If you plan on trading this may not be practical but in that case I would limit your exposure and read more about the risks.
Thanks eroche I think I have worked it out. I was just looking to transfer my steem into bitcoin etc. and which was a good exchange to use. As I am new to this I don't always explain things well but hopefully I will improve in due course. For now however I will just leave my funds in steem and steemit as I would just like to own some crypto in case of a financial collapse. Not that the little bit that I currently own will do much. 👍