At best I can list professions on a scale of Utility vs Difficulty to use.
At the top of the list is Guardian. Active defenses are strong in this game, and guardians have access to a lot of them. Can be easily traited for personal DPS, group DPS, group support and personal survivability without having to switch gear. Optimal gear set is Berzerker/Solider mix, both of which are very easy to obtain.
Second is Warrior. Tanky by default, it gives you more freedom in gear choice without heavily risking survivability. Easily geared to do respectable damage in almost any build, and access to a lot of passive support and group buffs that focus on damage enhancement. Their only minor weakness is lack of condition clearing.
Third is Elementalist. Ele as a class is about learning skill rotations. High power output, high support output, and an almost endless kitten nal of skills at their disposal. Their major weakness is their squishy nature, but learning to dodge tends to take care of that.
Fourth is Mesmer. A little harder to build for, but Mesmers are the kings of utility. The Shatter mechanic is a bit difficult at first…. but once you learn the cadence for set ups and shatters, they become one of the most dangerous (and useful classes) in PvP and WvW. They’re only slightly less dangerous in PvE, as their DPS is very Burst oriented. Their also rather painful to level early on, as the majority of their attack power comes from trait synergy- but their powerful utility skills (namely Glamour) will add a lot of survivability as you gain them.
Next is Engineer. High level of utility, but has a steeper learning curve from needing to memorize and organize kits. Does respectable damage, and is one of the easier classes to build Condi for- as their all ranged on this class. Its also impossible to top the flame thrower when it comes to tagging in K-trains.
Next is Thief. This is the line where difficulty scaling climbs. Thieves have very high mobility and burst potential for both PvP and PvE. Tons of stealth and teleports make them a hard target to track, effectively giving them free reign of an area if stacked correctly. Their down side is coordination…. you need to be adept at target selection and ground targeting in order to make the most of this class. (For those that don’t understand what I’m saying….. reaction time, finger coordination and mouse tracking on screen are not easy for some. Without those, thieves become rather limited.)
Next is Necro. While not difficult to use overall, they are difficult to get the kind of damage output the other classes are capable of. This will probably change with the HOT Reaper specialization- but for now they feel limited in PvE. In PvP and WvW, their Mark skills and high survivability make them very effective, provided you can get handle on Death shroud and Lich Form.
At the bottom of the list is Ranger. This profession has very poor build coherence, which makes it very limited in a lot of areas in the game. In PvE their main redeeming quality is a high degree of passive durability, and a pet that can do some tanking against Trash mobs. Damage output is somewhat respectable, and some of the sword builds can be quite impressive; but other then the Power Ranger builds, they can’t quite push up to the levels the other classes reach with relative ease. Their pet is also a liability in high end PvE content, as they die constantly and tend to draw aggro at the worst possible times. That said; there are a few niche roles they do well in…. Driver sniping in WvW, sustainable condi, and are considered a high floor PvP class.
Usually Guards/Eles/Warriors have good spots in every groups.