Which is the best Guild Wars for solo play? I need a good choice for my money. Please give reason as well.?

I am a solo type of person - I dont like co-operative very much. I have heard that Guild Wars is Co-operative but the benefits of playing the game outweigh the negatives of cooperation. What is the best chapter for soloing? I need to decide soon before the coupon i have for any Guild Wars game 50% off expires. Please answer. Which is the best for soloing?