For those who don't have much experience doing WKRs, there are two approaches to doing these.
The first is to focus on the main monster. PLD, WHM (curing PLD) BLM, SCH, SMN, RNG, COR and BLU (and some I'm probably forgetting) do very well at this; basically tanks, nukes and ranged attacks. However, many of the mobs have powerful AOE attacks (particularly the newer ones) which can quickly take out people meleeing.
The second approach is to spend your time killing the fodder mobs that will endlessly spawn throughout the battle. Most DDs will excel at this, and while it does not do much to advance the overall course of the battle (besides keeping mobs off of the tanks, nukers and ranged attackers) but can generate a lot of bayld and exp--in longer battles, it is possible to cap these out pretty easily.
Honetly though, you may not want to decide your job for these based on exp and bayld returns; the exp is fairly minimal, and can easily be generated through any number of other activities at a much faster rate. The bayld isn't bad, but again, can be generated much faster through other means (coalition assignments, lair revies, etc...) The real returns are the drops on completion and KIs awarded for the event.
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Renatus (Titan)
"We are Dragoons, and to make short work of foppish cavalry is our bread and butter."
-Bob Shaftoe, The System of the World