TouchWiz is basically the launcher, so install Nova. Or Galaxy Launcher. Or Go. Or Aviate. Or Solo. Or ... any of the dozens of free launchers out there. And see which one you prefer. (I've been using Nova for years - can't stand TouchWiz. My wife loves TouchWiz. And black olives, which I can't stand. Launchers are a matter of personal taste.)
If you want a different ROM, which is best depends on what you want. (Which is the best flavor of ice cream?) Do you want speed? More time between charges? (The two are pretty much mutually exclusive.) More internal storage space?
The best ROM is the one that gives you the most features you want without taking away features you need. (For example, some ROMs a few years ago were great - but didn't support GPS. Which is fine if you never use your GPS, but that's not the ROM for you if you need GPS.)
If you just want to flash a custom ROM so that you have a custom ROM, it's like buying a green shirt because it's not the same one as the same green shirt hanging in your closet - you won't gain anything but the ability to say "I'm running a custom ROM" without lying. (Oh, and you'll void any warranty you may have on the phone, and risk bricking the phone when you flash the new ROM.)