(edited by Lotus Bane.9387)
Better Choice for Trio
Honestly, pick any three class and you can make a trio out of them. A few pairings have better synergy (Thief and Ele for blasting AOE fields), but it really doesn’t matter.
If you’re looking for classes with a more unique playstyle, Engineer, Necromancer and Mesmer fit the bill. Engineers are particularly versatile with their access to kits/turrets/elixirs/etc. Could argue that Thief has a unique playstyle due to Initiative and no cooldowns (becomes a matter of managing your initiative to make sure you have the right tools when necessary).
I like the idea of engineer. Are there any viable elixir or gadget builds, with maybe one kit? I saw the HGH Hybrid build on meta battle. But is that the only viable elixir build?