I can’t give the best comparison, because my Mesmer is still lower leveled, but I should be able to give some insight. Personally, I see the mesmer being best at 1v1 since a lot of their attacks are single target (e.g. scepter) and their illusions focus on one target and when it dies they vanish. I know mesmers can be very strong, but something about their skills has always made me feel eh. Like using their sword up close just fields weird to me, even though it is a close range aoe. Also, while I don’t mean to say their attacks should be faster, they just feel a bit slow to me. Maybe it is just because it is lower level and at 80 I will see the balance behind it.
Eles may not be the best 1v1, but to me they have the best aoe. If you want to nuke foes from a distance, they can do that reasonably well. With the staff you can provide a lot of support between then 4 elements. I never did much with daggers but I know they are very mobile and can be very powerful when you get hang of them. Personally, I find the ele the most fun to play of all my characters. Whenever I am doing something on another character, I miss having the attunements. Air for speed boosts, water for condition remove, even earth for slowing down foes. I mean I have done dungeons on my guardian as well as my ele, but chasing around foes swinging a greatsword isn’t as interesting as dropping meteor showers and lava fonts all over (although both are probably just as effective).
Personally I prefer ele. Although if you don’t like idea of attunement swapping and frequently moving and casting, ele may not be best choice for you.
