I have a two-channel pedalboard that consists of an HX Stomp on one channel and a Boss IR-200 on the other.
For the HX Stomp, I have found that the stock cabinets really work well. Unlike an IR, the Helix cabs have a lot of different parameters so you can tweak the hell out of them to get different tones. You can still load IR's though...which works really well with the HX Stomp. I do load a few IR's for different purposes...mainly so I can get a particular sound out of a particular amp model (ie. make a Fender Reverb sound like a particular model).
For the IR-200, it's better to use custom IR's over the stock ones. The amp models are quite different than the Helix. Not as varied per se but with the EQ and other parameters you can really dial in what you're looking for with them. Add on some IR's and it's a winning combination.
For IR's themselves, I've tried out quite a few. Problem I found is that it's hard to try out different ones without the whole process of syncing them to the device and then clicking through each of them one at a time. So I got a good IR loader app, specifically mixIR3 by Redwirez. On top of that, I got the complete Redwirez library as well. Granted, there are other libraries that are probably better but these are still really good. Combined with mixIR3, I'll run the HX Stomp or IR-200 to my computer without the IR part enabled. From there, I run it into mixIR3 to try out different IR's. Makes the whole process much, much easier.