Make it simple for yourself, just buy one and learn for next time.
Flick a coin if you like.
Personally, for my first telescope, I didn't care too much about practical reasoning, I wanted a telescope that looked like a real telescope, and the biggest I could afford. That's just me. And hence I say just pick one, any old one that you happen to lean towards for whatever impractical reason as both 10" and 12" are great!
Roger.