imo, the classes I would want tazic over synapse on is:
Hunter
prot/holy pala(not sure about ret)
priest
Shammy(if not enhance, though not completely sure about that either, someone with more exp can clairify)
Destro lock(no clue about the other 2 speccs, maybe aff would want synapse?)
Balance druid(feral needs synapse and resto might even want the spinal health thing(hi jicz))
On rogue, warrior and DK I want synapse all day
But this is just my opinion and how I like to play it...
Double/tripple tazic is so op in arena so...