After the step-up of Safari on iOS 7, I've actually strayed away from Chrome since the load-up time can take about 5-8 seconds on average for me. But Safari on iOS 7 aside, Mercury is on the top of the list for me. Chrome and Photon are runner-ups.
If you're looking for free ones, then the top 3 I would recommend would be Mercury (there's a free version and a paid version), Chrome and Puffin (if you're looking for a flash browser)