Actually, I was happy with the Ace, but it was (if you use a few apps and from time to time on the Internet is) often overwhelmed. But I think in comparison, that the Ace is better in the hand and is more manageable.
Anyway, I'm quite satisfied with the S4, although the current price difference to Ace is very very big in my eyes.
What sound quality, camera, memory, speed, etc. As for the S4 is really recommendable.
What has me first very disturbed, was or is that you can have many pre-installed apps and settings do not disable or delete. That annoys me really very much if there are 30 apps on it that I do not need but can not uninstall.
Somewhere under the dash, 4 stars and recommended. Comparisons and video instructions are available on video-sharing sites.