I think the question is wrong, because I find a combination of browsers for different purposes is best.

I don't think the default browser is that bad, and I use Tear when possible, but it doesn't work well for Yahoo Mail for me. Fennec is fun for testing and I have actually found situations in which it was the only thing that worked.

So, why choose? Use everything! Get a 16-gig mmc card if you are short of memory, and learn to boot from it -- it's not hard.