Too many choices and none really matching. For me personally, I believe that it depends a lot on player's mood, objectives, needs and external boundary conditions (including real life obligations that will determine how far we're in peace and how much time we have)... All in all, I can summarize it that way: if I need to be solo on one day, I play another game than GW2, that is no RPG.
However, as a complement: on my opinion, others around are never a disturbance. If one wants to play with you but you feel to be solo, then you can just gently tell him/her. We have a good community in this game, with respect (apart from some trolls over weekends). Also, if you want to be solo, there is no obligation to answer to those asking for help. And at the top of it, in this game, players are no counters to each others (if you cut a tree, it's still there for others who want to cut same tree), so we're really entirely free of our way to go without to bother much about anything around us. Sort of full freedom. :3