I think the 45mm Olympus is nuce, and I've seen good reviews of it, but I'd just look at reviews of all supported primes for myself if you're unsure what to get. These lenses have been around a while and there should be plenty of reviews.
The one thing I'd watch out for with the
I2 specifically is that while a lot of people like the 25mm Olympus, I've also seen a number of reports of the left side of the image being soft sometimes.
I don't know if that's a hardware or software issue with the
I2, a problem with some individual lenses, or maybe even a design issue with the lens that makes it less suitable for use under the forces generated by flying it, but if you buy one you should definitely test it.