What class depends on your own stlye of playing,if u are the type who love to heal and feel good when ur teamates live at the end of a huge battle,then thats ur choice.
If you are the ones who love to be in the front of a battle to do melee and love heavy armour,instead of at the back casting spells,than choose a warrior.(but of course,u will deal lesser damage than any other classes,but u can take lots more damage than other classes. =) best warrior to start off is a Warrior/monk,as u can heal urself while taking damage.
I would recommend you to buy the Guild wars guild book as there is hella lots of good information for a newbie,also,for a veteran player in the game,u will be needing it,when u start the game,till you finshes it.