The consensus I have heard about espers were that the class doesn't really feel right until 30-35ish, but after that point they are strong and the movement issues are mostly gone.
The classes are head scratchingly unbalanced in terms of how they progress. If you want a good newbie experience, try stalker - they pretty much explode out the gates at level 2.
Medic is also decent start, warrior is still pretty terrible at 15, engineer is terrible to start with and becomes great ~15, haven't tried any of the others really. Spellslinger was so horrible at the start I couldn't continue ;p
For a quick path review :
Solider - the experimental weapons trials are almost always really useful, weapon crates suck, and all the other activities are relatively painless. Probably a good one if you want to progress without sinking too much time into it. Skills are not usable anywhere they are useful, so are pretty much trash.
Settler - the buff machines they build are fantastic. They add enormous utility by building taxis and shit everywhere as well. Gameplay is terrible though, it's like a never ending pickup items quest. Finishing zones will take a decent chunk of extra effort over levelling, but at least you are making other people happy right ? ;p Skills include summoning 1hour buff items and vending machines. No complaints there.
Scientist - if you are OCD this path will quite possibly kill you. Scan everything everywhere endlessly. They get to open some locked areas and do various interesting stuff with computers, like hacking enemy turrets and making them fight for you. At least you can have the scanbot scan stuff for you while you are running around. Never came close to finishing any zone after the first one, this one is a brutal timesink. Can summon group members to them, which is likely to be very useful, but has a retardedly long cooldown.
Explorer - this one is straightforward - if you like climbing on top of things and jumping puzzles, why not get rewarded for it ? It has the hardest missions, at least for me, I failed a few of the jump puzzles etc more than once. They seem to get the most hidden areas to themselves, which makes sense. They also get turbo speed boost flags all over the place - group members can follow you through them for the speed boost. Amusingly the flag effects stack until you are travelling at warp speed, which is a good way to die from falling damage ;p Speaking of which, their skills are shit - 15% less falling damage ? As an *activated* ability ? With a short duration and ludicrous cooldown ? Riiiiiight.