If you're a Coinbase user, please don't use Coinbase to buy. The fees are really high. Instead, use GDAX. Your Coinbase account is sufficient to register with GDAX and all your privileges like limits, KYC, etc. is carried over.
It supports both Market Orders and Limit Orders. Transfers from GDAX to Coinbase are instantaneous and off-blockchain, so there are no fees.
As a bonus fun fact, if you transfer BTC from GDAX to your personal wallet, there is no Bitcoin network fee charged to you. However, if you use Coinbase, you'll end up paying a lot more in fees than you must because Coinbase uses very inefficient fee-estimation systems and still haven't deployed SegWit or batching which would reduce network fee for their customers.
It supports both Market Orders and Limit Orders. Transfers from GDAX to Coinbase are instantaneous and off-blockchain, so there are no fees.
As a bonus fun fact, if you transfer BTC from GDAX to your personal wallet, there is no Bitcoin network fee charged to you. However, if you use Coinbase, you'll end up paying a lot more in fees than you must because Coinbase uses very inefficient fee-estimation systems and still haven't deployed SegWit or batching which would reduce network fee for their customers.