Advice for starting a new mesmer.
Whichever you find most enjoyable will be the least painful. I found it easy from the get go; the playstyle/abilities of Mesmer just sync’d with my kind of enjoyment. Some people swear by GS or Staff (etc), try them all and see what you like. By the time you’re level 10 you should have all your weapon skills unlocked and have a feel for what you enjoy.
As for how to level quickly: craft. It’s amazing how many levels you’ll put on just off doing a crafting profession or two.
Weapon wise, I would suggest trying all of them on your way to 80, spend a good 5-10 levels with each one. As when your in WvW, you’ll be running around with a full set of weapons (as we swap between them often in WvW)
Leveling quickly? – Crafting is the quickest way to level.
Otherwise, if your going to transition into WvW, why not jump in with a group in WvW (The exp you gain in there scales with your level, so its pretty quick!) and you get the bonus of practicing your Mesmer in WvW
Don’t rely on phantasms early on.
Don’t forget to get a green sigil of 25 stacks of power or precision.