Samsung galaxy y is a entry level android phone with lots of features. While the galaxy ace is a medium-end phone from samsung with a good value for money. Both phones have wifi,3g and gps but they lack secondary camera. The screen of Ace is better,pictures and videos look lively and colourful. But in galaxy y the screen is not as good as the ace. Colours look dull when compared to ace. Ace also sports a 5MP with flash camera which gave me awesome results. But the galaxy y's 2MP cam is not good in low light conditions.
Both phone supports motion gaming while the ace have an additional GPU which will make gaming better.
Samsung galaxy Y runs on Android v2.3 gingerbread while Ace runs on Android v2.2 froyo. But ace can be unofficialy upgraded to v2.3 gingerbread.
In overall rating ace is better than y. But if you are planning to browse more internet and play games then defenitely the galaxy ace is the one for you.
Battery drains quickly in android phones. So the battery won't last long if you browse a lot,watch videos and play games.
So another perfect choice for you is Nokia C6-01. It has a lot of features like 3G with secondary cam,WIFI,GPS and an 8MP cam with 720p hd video recording. Its screen is also nice. It runs on Symbian Anna OS and can be upgraded to Belle OS.
If you want to stick with android, then the Sony Ericsson Xperia
X10 mini will be a good choice.