Start your project with the engine you're more familiar with, which seems to be jmonkey. Ogre is a open source engine, often a synonym for 'works most of the time, rest needs to be hacked in somehow, documention is not available or obsolete'. Sure, this is not the rule, but a major danger.
I want my game to be a proof of concept, something like a set of functional mechanics.
I would look into UDKtoo, which is a hi-professional engine with very good tool support and you can use it for free (ensure to read the license).