When working on ASP.Net MVC pages I use Visual Studio because really, what else can I use realistically? It's fantastic and I love the tools and helpers it gives me.

For Rails I use Sublime Text 2, not because it's 'more leet' but because it works just fine. Plus any IDE's I tried using just sucked and slowed me down for little benefit. As a direct result of using a text editor I memorized the Rails keywords and helpers instead of relying on autocomplete so in that sense it helps.