Warrior is always the easiest class to play on all games to date. Because they have many HP and defense. It takes more time to bring down a warrior. Just as simple.

Only after you played a warrior and learned how to deal with aggro mobs, pulling, etc.. you should pick another class. Im GW, I believe that the order (from easiest to hardest) should go like:

Warrior -> Monk -> Ranger -> Elementalist/Necro -> Mesmer.

And, for the secondary class the choices go like

Monk: adds endurance, keeps Alesia on the team for the entire mission/quest.
Elementalist/Necro: adds range and Area Damage.
Ranger: pets and bows can potentially complete any other class. But I believe the ranger are the most underused class as secondary.
Mesmer: If you like to ruin somelse's day with loads of pesky hexes, thats your pick.

Thats why you see loads of "paladins" (W/Mo). They are - by far - the easiest class to finish the game.