i will add my vote for Modo, very powerful modelling app. i have had it for nearly 12 months, and have only scratched the very surface. nearly everytime i open it, i find more cool stuff to use ( eventually).

btw Vintorix, you can retopo in Modo quite easily, just using the poly pen and a background constraint/snap.

zBrush is a great app, but it is not essential, and just because someone does not use or want to use it, does NOT make them 'forever an hobbyist' !!!!!