The HTC Desire C is a 3.5" screen, same as the Galaxy Ace, and won't feel big in the hand (unless you have really tiny hands).
If it was the original Galaxy Ace you were looking at, I'd say the HTC is the better phone simply because it is a newer version of Android (the phone is a year and a half newer), so more secure and with more apps available. In general, HTC's customisation of Android tends to be a bit lighter as well, unlike Samsung's bloat, so that will mitigate the speed disadvantage in the processor.
By all accounts the actual physical design is done well. I reckon you're safe with it (though I have no first hand experience of either specific model).
Yes, it was the original Ace- couldnt find the newer version anywhere. I do have small hands but hopefully it will be OK