I've had a bad time with ESO guilds. And, in fairness, most of it is a ME issue in ESO specifically.
I like PvP, but I like it organized. I like it appointment-based with groups focused on the group and dedicated to showing up. No, I don't mean that strange tyranny of telling you what gear to wear, every trait, and every skill to slot. You can be group-focused without becoming a BIS fetishist.
I prefer teammates with extensive life experience and an abiding enjoyment of the written word. Folks who've gotten over themselves long ago and thus find humor in the opposite. People who can laugh at their own humiliating wipes in Cyrodiil. After all, wipes are inherently hilarious.
Finally, people who play for the experience of the game and the group, not the game-assigned experience...the XP. Not the rat pellets. The Skinner Box mechanics. Not the flashy mounts that tell everyone you're there or the loud recalls that tell everyone you're leaving.
In short, a crew of smart and sober souls with wicked wits.