After reading your post, I assume two important factors. Either it's a space saving thing, or maybe your going for the portability? In which case, both synths offer one or both of this. I've kind of had experience with the Microkorg, in the form of the MS2000. Here's my honest opinion:
In truth, you couldn't go wrong with either! The Microkorg is tried and tested. As a huge fan and owner of the MS2000, for me it would just work. The Mininova appears to follow the same kind of small factor and coolness as the Microkorg, whilst offering a few more interesting features. However, if I was in your situation, for me it would be a little bitter sweet. Here’s why:
When news of the Mininova first appeared, the first thing I did was checked out it's specs. After reading about it and feeling impressed, I could not help but then feel a little disappointed, after failing to find the magic ‘b’ word, yep you got it - batteries (dunno if I skipped over something, but no sign of that word - can someone confirm this?) Oddly, it’s a feature I’d personally look for first with something like this.
That means, if I wanted to buy the Mininova to take out and about with me, I’d need to take my laptop (for usb power) or be near some power supply! With the Microkorg, I could flip it into a cute carry bag and gig anywhere I wanted without anything else, well, except for some form of monitoring of course! (I’m the kind of guy who would take the microkorg to some random field and just sit and absorb some inspiration) but I’m just a geek...
On the other hand, if I wanted a different sound, newer features, and just wanted to be different, the Mininova would be a yes. It looks cute and interesting. I have experience with the K-station way back, and can confirm Novation is a great and quality company. For me though, that lack of battery power is a little nag! Hmmm ^_^