I use them all, and I prefer Firefox, how do you mean it's starting to run slow?
I use FF but I must confess I have noticed it leak memory in the later versions. Saying that I do have 50+ tabs open at the same time usually. Not noticed it is significantly slow though.
I can't get on with Chrome and unfortunately IE will be a necessary evil due to certain sites I use for work only compatible with IE.
Chrome all day long mate. Especially with Ghostery add-on![]()