Just a few words on the classes I found that lvl up easier for me.
I have played most of the classes this this alpha and found that whipper and shadow walker seen to lvl up the easiest and fastest, also being able to solo run the dungeons the easiest for me anyway.
I really enjoy the medic as well but a had a little tougher time soloing the dungeons pre lvl 24.
I didnt get much time with a def but public chat generally stated that they were ok to solo with but lacking in the pvp portion of the game.
Sentinels in public chat as well as what i found seemed to be 50/50 on desired play. the punisher i played had awesome range killing ability but seemed a lil squishy in pvp as well.
All in all i have found the "alpha" test in this game to be very playable, exciting with nice graphics and flowing game play. I look forward to beta and open beta as well as the release,