I did see a significant reduction in startup time with the WAV format, it was pretty much instant. If delay is an issue, I think that's the solution, at least the only one I can reasonably offer.
I thought about the various sampling rates for MP3, but rejected bringing that up. If I open that can of worms, I'd get into a whole esoteric discussion about compressed audio. I think 99% of the audience for this product would be scratching their head and wondering what I was babbling about!