Ha... none. Because I try to stick with the same three fonts for everything!
Over the last 5-6 years, I have really loved the whole Gotham stylings and simplicity of the bold sans serif movement. Proxima Nova, Gibson and Museo Sans still tend to be the first three fonts I reach for in most projects.
These are my main reasons:
1. Clear letters
More than style, theme or creative spark, if the words you are displaying aren't clear then it's worthless.
2. Easy alignment opportunities
I look for fonts that are easy to kern nicely and have natural ways of "fitting characters" together. You could say I like it when character spoon well in a word! One of the best examples of this are the people who work on Jimmy Fallon's stuff, both when he did Late Night and The Tonight Show. They find natural ways for his "I's" and "L's" to align, and it's sharp.
3. My biggest focus: a clear variety of bolds
I like fonts that offer more than the simple regular and bold. I like to have at least four weights to any font I use regularly (thin, regular, semibold and bold). Having a 5th bold (usually called black) is a bonus!