What makes a guild "good"?

Depends on my character's class and how often I play my character. What I mean by that is, at lower levels, I'll put some of the characters that I play the most into a close-knit guild that I already know people in. Hence the reason for my Aran + NW being in Scandalous (my former guild). However, I put my lv 133 Night Lord in higher up guilds, specifically for Zakumming, HTing (some time in the future), CWKPQ, etc.

I play each of my own characters differently.