Hi Marco,

The only question is : do you have the time and the will to discover and learn Houdini ?
Because it's a very complex software, and you need to invest time (lots of time) in it to be rewarded.

It's not like you just buy a license, read the documentation and start produce amazing 'stuffs'.

In this learning journey, the apprentice edition is the way to go (and yes you can export .obj without any restriction as far as I know).
It's the most addictive software I ever used (it's more like a game than anything else for me :))

Beside, I hate subscription model, but 200$/year for the Indie version is an amazing deal ...