I only have experience with rangers and warriors mostly so I will talk about them. To solo rank make sure you chose a dex build. Ranger can solo rank very well, you can go to all the usual places and rank on your own, Aldevari, Forest Of Nowhere, Hidden Forest, Plains of Arendyl, Drogran Hills, Fridgid wastes, Dranetty woods, and Mountains, Headhunters.
Exploit vulnerabilities, ambushing an elf with a iron weapon that you get from the ruined keep will work just fine. (just watch out for vets trying out the Assassin Class for the first time :-), when I am trying out my first battle rager :-( haha) As a ranger you also have herbs, and camp which lets you heal quicker than most classes. Plus later on you will be able to use your own healing weapons, and wilderness familiarity. I have attacked many mobs just doing ambush, serpentstrike a few times before the tick, flee, camo, camp one hour. You are back on full health ready to go again. I would say that a dex ranger would almost be the best class to tank storm giants on the mount with. Some one once posted on officials that his last tier defensive shifter could not take those giants well at all. My last ranger I solo ranked on them, it was a hunter which was probably a better tank with archery though. I mainly play at night time Australia so the numbers are always under ten so I know how you feel. I sometimes feel I am playing this game by my self. I guess you can solo rank a lot of builds although I have not played them yet, assassin and bard I would think could do it. Also sometimes you are better killing mobs for a quick 250 exp than killing mobs that take ages, and hurt you much for 500. Lastly if you want to solo rank, chose human, the amount of experience between a human, and a giant in getting to hero would be astounding.