The character creation tells you a pseudo difficulty level of each class, but it's pretty rubbish.
Burglar - De-buffer, conjunction (Fellowship manouvre) starter. Crowd Control. Melee based
Captain - Buffer, resurrection skills, group survivability - Melee/shout based.
Champion - AoE Damage, off tank (can be Main tank in most situations) - Melee based
Hunter - Single target damage, taxi service, decent enough off tank for ranged mobs. Sub-par crowd control with right traits. Range based
Guardian - The main tank class, high armour/morale/mitigation. With the right traits and gear is actually a viable form of damage too - Melee/Shout based.
Loremaster - Debuffer, Crowd Control, Battery for power - Ranged fire/tactical ( a form of skills) based.
Minstrel - The main healing class, all sorts of skills for removing dread, increasing morale etc. Has some damage (nerfed in new book) shout/light based
Runekeeper - Hybrid healer/ranged damage, can play both roles via an attunement system, will expereience a lot of 'balancing' in the near future. Ranged fire/lightning based
Warden - The new tank class, wears medium armour, gains threat via leeching other members as opposed to force taunts. Melee/ranged combination
That's a basic overview of the classes. Out of the above the most straight forward are champions and hunters IMO. But funnily enough, they are the most common and badly played. A lot of people say those classes are 'easy mode' when they just haven't met a good player.
As already suggested, i'd try them all, you get plenty of slots and they are per server so using 2 servers you can have every class.