for a char just for pre i would go W/R with a pet or i always liked E/R or Monk/R
but the most used i have seen with legendary defender of asconld is W/R or E/R
Mesmer. Very strong self heal due to recent buff, and good armor ignoring damage from empathy whilst allowing you to hide behind walls, can also degen things to death. Very good pre-searing char
warrior provides highest armor at no downside you dont need the energy.
both professions provide an amazing self heal
enough weapon mastery to wield the goty bow or other weapons
It's presearing... there is no bad combination to pick. some of us never even bother to take a secondary. You can dominate the play areas with any of the classes.
I've gone about very effectively as just a necro, just a ranger, just a monk and just a mesmer.
But if you are doing this with LDOA in mind, take the time to study a few of the guides people have done and take to heart rules about not questing until you are about maxed out.
3 choices : If going for the "big preys" (charr mostly, thought there are some mini bosses) : Mesmer have the best 1 target kills.
If going for mass kill : Monk/Elem, the only ones with aoe (ok ok wars have 1), monk also get heal breze (unique to Mo/) and sheilding hands (dmg reduction), sometime meaning invincibility.
If going for Epicness : your choice, most classes can kill chars 1 way or another. I personnally see the most "classic/epic" pre sear class as necro and mesmer.
N/R ...I have a level 14. I'm hoping to someday get LDoA, but no hurry. I kinda dig having a pet and minions to do my bidding while char hunting. But like others have said, it really doesn't matter what you pick, just pick what YOU like. If you are hoping to achieve Legendary defender of Ascalon, here's a handy guide for the basics: http://gw.gamewikis.org/wiki/Defender_of_Ascalon