As has been said, find something you enjoy. As far as the "best" class, a lot of them have pros and cons.
Mage and Necro get great pets with their later epics. They do great DPS but cannot tank the high end stuff.
Warriors are great tanks (duh) and PLers, but the PLing only happens when you are rather high end and get the AE DD augs available to them.
Pallies are a good all-around helper class. Epic procs a group heal, good survivability but obviously not great DPS. A good tank class to consider in a multi-box setup, but they're not as great in the high end raid content as tanks.
I really enjoy my Monk, but their epics leave something to be desired. Great DPS, they get eaten alive by AEs and Rampage in high end, and half of their epic effects are useless. The clicky adds a rapid-firing proc, but the focus and flying kick mods don't work.
Bards are underplayed and can be very handy if you plan to join a guild fighting the higher end stuff. Just be aware charm is cut out of the game at the moment due to exploits with it.
Wizards are generally laughed at, from my understanding. They're not good to multibox, and their DPS is a joke compared to a Mage pet. I'm not sure how they stack up these days with the added spells in the higher end zones, though so I could be wrong.
Beastlords are another viable pet class, but again their pets get eaten alive by the higher end AE and Rampage.
Rangers and Rogues are great "autofire" DPS for a bot squad and/or a guild that does high end stuff.
Clerics are good as core healers, but their epics aren't as good as the Druid and Shaman. The latter two get no rez on this server, but their epic effects are solid. Druid = big HP regen, Shaman = big HP buff.
Enchanters... well... with no charm and crack buffs available at a hail, they're generally not played either.
===Classes you want===
Monk = DPS (Best DPS end game)
Ranger = DPS (Best until monk gets end game)
Pally = Group Heal (always a good class =D)
War = Oh so overpowered tank, good for everything (9/10 people you meet will be a war)
Cleric = 42k group heals with a 1 oracle. you decide.
===Support Classes===
Shammy = right click epic, logoff (RoA must)
Druid = right click epic, logoff ( RoA must)
Enchanter = right click epic, logoff
Magician = CoTH, only use
Bard = stacking DS, 2nd best for RoAing behind warrior.
Rogue = Good DPS if your one boxing, otherwise use a monk.
===Everything else===
SK = Great for soloing, terrible in groups = unwanted
Zerker = no real reason to make this class.
Wizzy = bad dps until end game around T3 where they get a decent spell, still not worth effort.
Bst = Good dps using disc but doesnt last long and caps pre T1
Necromancer = Yeah just dont make this class.
Just thought we needed a little clarification of these.