We don't have a group comp at this time. When we start running a steadyish group, that's something we can do.
For roaming and havoc, with recommended professions bolded:
Necro - Scourge seems popular even after the nerf. Reaper is, I'm sure, still nasty in WvW.
Mesmer - condi roamer build when solo; for group, maybe would go with more of a power build with tricky utilities mixed in
Elementalist - healing auramancer for havoc; not sure on weaver roaming yet
Ranger - Soulbeast seems popular but I keep killing them, soooo (honestly, well-played vanilla rangers give me fits)
Thief - Daredevil; not sure I'd take a Deadeye to havoc
Engineer - ?
Warrior - Spellbreaker is pretty op, but I've been crushed by well-played Berserker specs for months.
Guardian - Firebrand. When in havoc, probably want to sprinkle in one or two stability skills.
Revenant - My preference is condi rev with boonshare for havoc and power rev for solo.
But, really, take what you're most comfortable with or what you're most interested in.
Semi-relevant info
Owinn (Samis), Olsi, Casi (GrimRiddles), Jak, Aurelious, Science (scarecrow), Dbunny (ZerotheFang), and myself (Aleph) have all run havoc. Additionally, I know that you, Ravem, and Shant have expressed interest in havoc.
Of these members, here are the classes I remember seeing for WvW (sorry if I misremember something):
Owinn - herald
Olsi - firebrand, warrior
Casi - necro
Jak - thief
Aurelious - ranger
Science - necro
Dbunny - necro (?)
Hrom - herald, spellbreaker
Jinn - undecided
Ravem - soulbeast, firebrand
Shant - guardian
Also of note:
Erin - thief
Merb - guardian and, I think, herald
Slailie - ?