I like Coinbase (
https://coinbase.com/). You have to link a checking or savings account, which can take a few days. Once that's set up, there's a waiting period of 4 days before you can buy or sell. After that, you can sell or buy BTC for a 1% fee, with the money directly withdrawn/deposited to your linked account. They allow you to sell up to 50 BTC a day.
I also use coinbase, been very good so far, I linked my bank account and it took about a week if I remember correctly. Each purchase is via ACH so it takes 3-5 banking business days to transfer your funds to purchase.
It takes 30 days for a fully verified account to reach the buy/sell of 50 BTC per day limit, although the initial 10 buy/sell BTC per day limit is more then enough for most folks.
Main reasons why I like them:
1) US Based
2) VC Funded and Backed.