OpenFOAM vs FOAM-extend: poll on usability
 

Which one is better to use?

Based on what? Surely it totally depends on the case in question, for example foam-extend has some features OpenFOAM does not have like 'out of the box' solid mechanics solvers and immersed boundary.

I agree with Lee
I have like 11 different OF versions in my OpenFOAM dir (including 1.6-ext) as well as foam-extend-3.0/ and foam-extend-3.1/ in the foam dir.
I use them all, and it just depends what saves most time/is most easy + other factors.

J.