OK well, so there’s a lot of things you are asking here, mainly because there’s a pretty massive difference in group play between Fractals and Raids for instance.
I suppose it would be best to go with the simple roles that each profession does, but bear in mind that although you might be asking for the most optimal setups, none of the high end PvE content requires you to run those setups unless you want to speedrun competitively which for what you guys want (coming back to the game fresh), might not be the best thing to start with.
Warrior: Might Generation. Due to Phalanx Strength, Warriors are the top slot for generating Might for the group, they will contribute most of the might without the need of fire fields. And with Might being pretty much a must-have for melting bosses quickly, you will see either the Power Variant or Condition Variant of the PS Warrior in each 5-man group (meaning two for raids). Also Banners.
Mesmer: Quickness/Alacrity Generator. Mesmers have a similar role to Warriors, but Mesmers lose in the damage department, which is why you will see Chronomancers going ‘Tank’ for Raiding, or simply ‘Damage’ for Fractals. Despite the low damage, Chronomancers have the invaluable Quickness and Alacrity buffs that are must-haves for any comps, plus their lack of damage is made of for several utilities for any type of encounter. A good mesmer can carry any group.
Elementalist: Raw Damage, Elementalists are kings of Power DPS. Large Hitbox monsters and swarms of adds crumble under their DPS, but a lot of the elementalists power relies on buffs from the group. A Disclipline Banner + Fury Buff will make an Elementalist very happy to break DPS records, but because they lack a lot of everything else, you want to cover those bases first.
Necromancer: Originally the Kings of Condition DPS, but they have gotten a fairly unjustified nerf, which actually did not hurt their spot in group content. Mainly because although they don’t come close to Elementalist DPS numbers overall, Conditions and Epidemic are their bread and butter for debilitating and destroying monsters. They are especially wanted in Fractals for Epidemic Spam, you will see ‘4 necro 1 druid’ condi groups quite a lot. Still, given their current state, you could get away with in Raids running the much more harder to play Condi Engi if you want a slightly higher condition damage edge in certain encounters, but Necro is a safe bet.
Ranger: Heals? HEALS! Druid is a solid pick for healing, and spirits are a unique buff like Banners to increase the group DPS. To put it into perspective from here, the current raid meta is Two Warriors, Two Mesmers, Two Rangers, but there are variances based on the encounter, you might roll a single Druid for instance!
Guardian: Upper level damage, and a reliable way to have Protection in your group. The group won’t feel any offensive buffs from a Guardian, instead Guardians will help ensure everyone is feeling the heat a lot less. Healers will like Guards, well except for Tempest Healer who can do their own Protection, but that’s a specific build I don’t cover here
Engineer: You have to feel for engineers, they are hell of a lot of fun to play, they have just as much tools as Mesmers do. Yet, despite all of that, the ‘Meta’ has phased them out as they are like a Jack of all Trades without providing group buffs. If Engineers could provide a trait with group buff raising Condition Damage by 180, something like that might be enough to push them more in use. Well, at least you can all watch pro engineers solo hard fractal bosses.
Thief: Close to matching DPS numbers with Ele, and a good supplement to a Raid comp needing a bit more CC with passive Basilisk Venom applying to nearby allies. Not a bad pick if you want a melee instead of a ranged DPS for an encounter, plus you can’t argue with that flip!
Revenant: A recent change to how key offensive boons functioned has utterly decimated this profession from even normal Raid comps. It’s not as if it were a bad idea to take them, but in the slot they took would be some key buff missing from the group in exchange for CC you might not need, Fury you already have, and/or DPS you really want. Mind you, this is the ‘Raid’ mentality here, Fractals are perfectly fine for the profession.
I hope this helps.
Thank you SO much! Could you also give me a short preference of desirability!? For instance (just my random ranking, not accurate or anything, just a example)
Support( heal, or buff): #1 druid heal #2 guardian defenses buff #3 warrior might fury
DPS Raw: #1 elementalist #2 thief #3 warrior #4 guaridan #5 ranger
DPS condition: #1 engineer #2 Necro #3 condi ranger
Tank: #1 Mesmer #2 guardian #3 warrior
something like that
i will then make a more summarized version of your entire responses into the post in case any new players have the same question!