Personally, I like the smaller size of the M because it allows me to type with one hand. I came from a larger handset (galaxy s2) which had a big, beautiful screen (but really only a bonus while watching tv on it). I got used to the size of course, but it was a two-handed deal. I also go walking/hiking with my phone while streaming music and a smaller phone is ideal for holding while moving (and not dropping). Things to consider I guess...besides the usual do you put it in your pocket stuff.
If you're concerned with battery life, check out my battery thread. I posted screen shots.
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