I've not had any complaints using Gemini for the last year. They have been brought down once by the increased volume (two months ago), whereas coinbase goes down every single time there is a price crash. I'm sure a lot of that has to do with the amount of users using coinbase vs. Gemini, but I'm much more confident in the twins' ability to scale their business based upon my experience with them thus far. They run their business in a very professional manner.
Plus, they offer 30 free btc withdrawals per month. Something they have continued to honor, despite very large fees of late.