The Galaxy S has three HSDPA bands: 900 / 1900 / 2100 and gives maximum speeds upto 7.2Mbps while the Galaxy Ace has only two HSDPA bands 900 / 2100 . Wi-fi bands are the same on both the phones supporting the latest band of Wi-Fi, the 802.11n and 802.11b/g as well.
GPS is available on both the phones and Bluetooth is 3.0 enabled on the Galaxy S while the Galaxy Ace has Bluetooth 2.1 with A2DP support.
Operating System and UI:
Samsung Galaxy S i9000 has a latest version of Gingerbread, 2.3.3 with Samsung’s User Interface, Touchwiz 3 and the Galaxy Ace comes with 2.2 Froyo but the 2.3.3 Gingerbread update is coming soon. The User Interface is the same on both phones though the Galaxy S provides an overall better experience on Gingerbread, thanks to some minor tweaks and improvements for the larger screen.
Battery and Processor
The Galaxy S has a 1500mAh battery. The Galaxy S claims to have around 14 hours of talktime and 713 hours of standby time on 2G while the Galaxy Ace has a 1350mAh battery and around 11 hours of talktime and 640 hours of standby backup.
The i9000 has 512MB of RAM along with a 1 GHz ARM Cortex-A8 processor, a PowerVR SGX540 GPU and a Hummingbird chipset while the Ace S5830 has a 800 MHz ARM 11 processor powered by a Adreno 200 GPU and Qualcomm MSM7227 chipset.
There is a price difference of a few dollars but the Ace is the best bet if you’re keen on the budget and looking for a portable phone which can perform really well. The Galaxy S, slightly bigger in size comes with a more powerful processor and a better Android experience overall. Stretching your budget a bit and going for the Galaxy S i9000 would be the best option as the software updates and overall media enhancements and features will only keep becoming better as time progresses but Samsung might not be keen on the Ace.