Several years ago I used to use Opera as my main browser, but I found it doesnt cope to well when it comes to media such as Flash, videos, broadcasts. Granted this is a few years ago and things may have improved since, but it was enough to put me off, particularly when chrome was so much faster. These days I stick to FF and chrome depending on what Im doing.
Oh and of course safari on iOS. Personally I think chrome is the most lightweight, but I like some of the add-ins you can get with FF, which is why its still my main browser.