A launcher is basically a new UI, it just overlays the current launcher in place of the one you download.
There isn't really a "best" or "greatest" launcher because everyone has a personal opinion on them.
I will give you a few so you can get started and check them out:
Nova Launcher
Apex Launcher
Go Launcher EX
You will be able to keep your wallpapers through this change, it might just change them, but you can always change them back
