Mage gives you COH - which can move bots faster, help on bad pulls and more...., DS, DPS, Pet DPS, summoned items for pet and players (somewhat of a bonus now), Debuffs (though shm would take care of this) some areas pet can act as offtank.
(mage is just dps - all due respect, its a bit more
)
Necro would provide FD pulls, snare, mana regn boost, high cost rez, Ability to kite
Druid means ports, evac, snare, DS, DPS, Back up healer, Mana regn hp buff, and Ability to kite - more adds perhaps- if situation proves necessary...
Wiz means DPS, ports, evac, snare
W/ever you decide you have a couple options - its not really a one size fits all answer- what's best its what works best in your trio... my mindset I'd never be able to play wizard mostlikely because I'd over do it killing them repeatedly.
For example even a melee dps could be suggested, but caster would be naturally easiest to posistion and get the most from.
Courage is resistance to fear, mastery of fear - not absence of fear.
Mark Twain
US humorist, novelist, short story author, & wit (1835 - 1910)