I use both along with AdBlock Plus. NoScript should cover you in general, but there may be a site where you want to enable js, but block Flash. No reason not to use both.
Once you install NoScript you'll be amazed how many extraneous, external site scripts are loaded on most sites. It's an extra step to enable js on your regular sites, but once you've done that, you only have to occasionally pay attention to it when you're visiting unknown sites. You can usually navigate most sites without bothering to enable js at all.