I prefer emacs for editing text, but modal vim-like interfaces for simple tasks such as browsing a document (zathura) or the web (vimperator).
I switched back and forth between vimperator and pentadactyl many times. Pentadactyl is a bit more complex, and used to break often. Perhaps it is no longer the case?
I haven't seen pentadactyl break anything in a long time, but then I run a very vanilla setup. I'm the current maintainer of pentadactyl-git on AUR; if you try it and have trouble you can always ask in the AUR comments.
I switched back and forth between vimperator and pentadactyl many times. Pentadactyl is a bit more complex, and used to break often. Perhaps it is no longer the case?