Both are great phones. Not to muddle the waters, but the HTC One M8 is also a very good phone (I have one and I love it), but really it boils down to personal preference. Both phones are very good. Personally, I would go with the Xperia. I've had the Galaxy 3 and I know people who have the 5. It's a perfectly good phone. Both have pretty similar specs (check Cnet reviews), but you won't know for sure until you go to a phone store and play with them both. Play with them, hold them, put it in and out of your pocket. Buy what feels comfortable.