Absolutely nothing's wrong with FF, but there are sometimes reasons to use chrome. Different browsers, different bugs, after all... :]
I normally use FF, but there are situations where I use chrome instead (both very up-to-date versions, so more or less as good as they get).
chrome uses more memory on average because of the multi-process architecture, but that architecture also makes user-control of memory usage much more convenient, because closing a tab with a memory-hog page in it immediately releases a hefty chunk of memory (whereas this usually isn't the case with FF). So sometimes when my memory is running low, I'll use chrome, despite the higher average memory usage, to get the increased controllability.
There are also cases of bleeding edge html5 stuff where the chrome implementation works better. E.g., both seem to support webgl in general, but some webgl-using pages only work properly in chrome for me.
It's really nice to have available two completely independent implementations of a modern, featureful, robust web-browser... Before chrome, there was [on linux] basically FF and a bunch of toy browsers, and the latter were often not very usable for many pages.
