With 16GB, you begin to see the end of the tunnel, with a margin of safety that is felt in transport / travel.
Unfortunately, Sony has chosen the priority size and it pays. As lon is 20 micro SD card 32GB, 16GB for your Vita will pay more than 30 (still cheaper than in other stores, that they are in line or physical). Logically, this card will be specific to the Vita and may not be used for another purpose.
Moreover, it does not seem to shine by its performance. Too bad for a portable console that's worth it, having to pay for games / accessories (including a mandatory memory card) so dear!