Honestly though, solo play is what you tend to do for >90% of the time. Waiting around for someone else to finish a heart area you've already completed is a slow way to level. A decently built and geared character can solo the champions for skill points too. Dungeons is where parties are really needed, not much else. Unless you're planning on WvWvW, in which case you don't need a party, you need a zerg.
Yeah, this is something I'm starting to dislike about the game. Grouping seems very.... counter-productive.
I played with 2 RL friends for a while and heart quests were just silly. We were basically just solo'ing in the same general area, if we tried to help each other out everything died so fast it was honestly just not fun. The dynamic events scale to number of people, so they can be solo'd too (most of the time), and anyway when they pop up a zerg of people tends to show up so again, your group is irrelevant.
Personal quest... solo'able, I don't know if it scales or not if you add more. Either way, there's lots of reports of it bugging out and not advancing if you do them in groups so I avoid it.
Dungeons don't even show up till level 30, and you only get a new one every 10 levels..... hard to justify doing the same dungeon over and over just so you can do something in a group especially since you can't really use the reward tokens till 80 and because the anti-farming penalty is insane - first run: 60 tokens. Second run: 20 tokens. Third run: I didn't bother, but IIRC it's like 5 or something.
Small PvP, I guess you can make a group for, though I don't do it very often I don't know what it's like. WvW is, as mentioned above, just a huge zergfest so while you can group... once again you're at the whim of the zerg.
I know the trend in MMOs is to make them grindy single player games where you group up with people every now and then to show off what you got from
the cash shop grinding your life away but it's kind of disappointing just how bad it is in GW2. At least in your average MMO normal monsters have enough life that grouping up to kill them at least makes it go faster so while it might not be the most efficient method, it at least does not feel like a total waste.