Firefox, I have used it for quite a few years now. Normally the Nightly version with Aurora as a back up for the odd occasion Nightly breaks.

Chrome is good, about the same speed as Fx Nightly on my computer, when it gets a side bookmark bar I will have a serious try with it. Yes I know there is an add-on (Neat Bookmarks) but it is not the same thing as a permanent sidebar and is more difficult to use plus it lacks the customization I like.