I've seen those mounting rings for putting singles in a pickguard cut for humbuckers, but I have never used one. I almost did when I was renovating my Jagmaster but I changed my mind.
I probably prefer singles. I prefer the clearer sound, and I feel they respond better to picking nuances, which is a huge part of my (so-called) tone. That said, it depends on my mood. If I'm feeling bluesey, I go straight for the singles, but if I'm feeling a bit more jazzy, I go for the flatter, warmer sound of the 'buckers.
If I'm using and overdrive pedal, it's a neck humbucker all the way.