Are you looking to get stock modules, or are you interested in venturing into the world of modded modules? The latter will be at least a little more expensive, but oh so worth it. If you want to try holding to stock modules, I can vouch for the Grail being one of the best ones. To me, it's early Rectifier tone with a little more of a Marshall midrange twist to it. That will cover the heavy side no problem. The SL+ is another pretty good stock module, but it has a ton of gain and if you're just starting with two, I think you'll need something a little less raging for your second module. The Tweed isn't bad. I've never played the Plexi, but some people like it.
Now, if we're talking modded modules, it's a lot easier to cover the bases. If I were only going to have two, one of them would definitely be either the SacredGroove or Jaded Faith XTC. I personally prefer the SacredGroove one and that's what I have now, but I used to have the Jaded Faith one and it's great too. The beauty of these modules is that you get a Plexi mode that can do cleaner tones pretty well, a blue channel mode for Marshally crunch, and a red channel mode for squishy high gain. Just one module really covers a lot of ground. For my second one, I might have to go with the Jaded Faith Voxless. That covers you all the way from clean up to quite crunchy indeed.