All comes down to which you like better. I don't know about Canon but the d90 is a pretty decent camera. Just do a craig list search from your area and check current second hand prices.
A piece of advice when buying from a friend, do not under any circumstance come back with any complaints whatsoever. Once you decided to buy it then pay for it right away and don't ever bring it up again unless to say how happy you are with it. IF 2 weeks later the thing stops working, well then be a man and just suck it up. A friendship is worth more than some piece of camera gear.