I choose Bard for my first UAT (main is paladin, actually suffered through to get a max det/par novus sword and working on a max det/par novus shield) mostly because that's the DPS class I'm more than likely going to play the most, even though I kind of have a pro det/anti skill speed bias from playing a PLD. If you play one of your other classes preferentially, and especially if you're still just using the zenith for that class, just get it for that class even if the upgrade's better for a different class. If your choice is between classes you don't play all that often, then you can consider things like which is (strictly speaking) better, or which will be good as a glamour in the future, or whatever. But if you're at that point, another thing to consider is to just bank the UAT on a retainer until the weekly soldiery cap is lifted unless you've really got 1300 soldiery burning a hole in your pocket. Then you could use the UAT to pimp out your retainers gear, or something.
