George Gibson cards for me. I like that there are different issues to kinda suit different moods, and even variations (mostly backs, but a few fronts) within those issues when I'm feeling OCD
As you noted, we all (probably?) have hot and cold periods. I find whenever I'm doing less collecting I do more baseball reading. No matter what I'm reading, it always eventually turns into reading about prewar baseball, and that gets me thinking about what prewar cards I have. Inevitably, that gets me looking at my collection, followed by poking around eBay, checking out this site, etc. That alone explains why I'm back posting after a pretty quiet past few months.
Cheers,
Richard.