I am guessing that if you really liked your hero, you loved HTC sense as well then, BigDannyO?
If so the new sense on the S/X is even better, more refined and just feels lighter over all. Touchwiz could put you off the GS 3 completely and that alone would make it either the X/S for you or heck even the new sense version might put you off completely, therefore leaving only the GS 3 as your choice
I personally hated previous versions of sense but absolutely love this V4, just a lot lighter than previous versions and more modern looking along with great features and the main things being the camera UI/features, dialer, gallery and calendar application which IMO no other android skin/app can come close to.
Touchwiz on the GS 3 is better than previous versions too and is tweaked better than sense in terms of gestures, battery life consumption, RAM usage etc. but I personally didn't like the modded apps or colour scheme throughout the UI and feel that sense looks more polished/sleek overall with a better colour scheme (even though white is not my favourite colour

) and has a very unified feel across the apps, widgets etc. and I prefer the menus, notification bar etc.
It is very subjective this now, as some hate sense and love touchwiz etc. but be sure to play with both phones first and trying all the apps out to see what you think regarding software.
Of course this may not be an issue at all if you intend on rooting and flashing a custom ROM or/and replacing every stock app with 3rd party ones.