I've played both. These are my general observations.
The Wren has a little bit better sound, especially on the lows, more power. The buttons are a little bit bigger on the Wren (For some reason they are really small on the Rochelle). And the position of the buttons is a lot closer to the handles being that its a lot smaller than the Rochelle. If you're used to a larger 20 button where the keys are higher from the handle you'll probably find the Wren a little awkward to play especially on the G row. Also the frame ends on the Wren is of lower quality. Some kind of wood composite. The Rochelle has a nicer finish.
The Rochelle keys are easier to get around on in my opinion even if they are smaller. I came from a 20 button that was around the same size as the Rochelle so the Wren wouldn't have worked for me. The lows on the Rochelle are disappointing though. Not very powerful. And the action isn't as good as the Wren's. But ultimately I went with the Rochelle. Both have their pros and cons. Its up to you which qualities are more important.
