I’d pretty much agree with Thaddeus and Roachsrealm.
Generally everyone can do general questing pve and boss chains. Some classes might be a bit weaker at this (generally lack of range on bosses like Jormag), but nothing that prevents you from being useful at fights and obtaining gold medal and loot.
So the 4 elements you can focus on are: sPvE (dungeons/fractals) / sPvP / WvW zerg and WvW roam.
sPvE: I’d say that Warrior / Guardian / Thief / Elementalist / Mesmer are all solid picks for this at the moment. The Ele and Thief provide very high dps. Mesmer very useful utility (time warp / portals), warrior can stack might for the whole group easily and guardian is generally good as defensive utility.
Engineer and Ranger aren’t bad either and follows behind above ones. They don’t provide much that the others can’t do though, except maybe solid condi damage.
Necromancer is quite unwanted at the moment in Dungeons / Fractals, on all but certain niche fights.
sPvP: Guardian / Elemental / Thief / Mesmer are top picks currently. The first for it’s ability to hold a point really well. The latter 3 for their high burst and good mobility.
Warrior and Engineer are good picks after that.
Necro / Ranger are a bit lower again. Not really all that bad, but they don’t really bring anything that others don’t do better, which is their limitation really.
WvW zerg: Elementalist (Seeing) / Guardian (patterns) / Mesmer (yet?) / Necromancer / Warrior are generally top for this. Elementalists and Necromancers bring the big AoE nukes. Mesmers often provide utility (stealth/reflects) and burst (shatter). Guardians and Warriors hold the frontline.
Thief isn’t as useful in the actual zerg, as it lacks range and AoE; however you always want 1 or 2 around to act as scouts, ahead of the group and watching the flanks. Looking for enemy zergs.
Engineer and ranger are both ok, but doesn’t bring anything as good as the others, but they do have strong single target burst.
WvW roam:
You can make anything work here. But generally classes with high burst, high mobility and is possible stealth work really well for roaming.
Elementalists, Mesmers, Thieves, Engineers.
Rangers work especially with traps. Warriors and Guardians are a bit worse, but work well with some backup.
Necromancers are generally not as good, due to lack of mobility; but you can make it work.
Final note: Every class works everywhere, lets make that clear. But there is a definite bias towards certain classes.
Elementalists / Guardians / Mesmers / Warriors are great in just about anything.
Thief is great in nearly everything; lacks a good long range option to be great at everything, but it compensates that with some other niches.
Engineer is good at most things; it used to be really kittenty but it got a lot better, but it’s still hard to play to its max potential.
Ranger got some buffs to make it better. It’s not as shunned as it once was, but it still has a lot of situations where it doesn’t bring anything that other classes don’t bring.
Necromancer is mostly bottom of the barrel at the moment. But it’s really really strong in WvW zergs and sees some good uses in sPvP.
