I heard interactive brokers don't have that good of a customer service, but if you're not looking for that definitely go for them. It's more like for advanced traders :)

If you have a margin account with etrade you can sell and buy right away. No waiting 3 days. Just do some research on a margin account so you know exactly what you're getting. Also, with IB you need at least $10K to open an account.

You need a margin account. Like Hebrew said margin accounts help to buffer the 3 day settle. Interactive brokers is for serious traders but they have higher income and experience requirements. IB also has a decent amount of borrows for shorts.