If i could afford it i would definatly go with mac, i think they are much prettier and smoother machines, since im not exactly a power user windows allways seems a bit jerky to me + i have allways like the quality of apple products.
Windows isn't bad though it does the job quite nicely ad iv never had any mojor problems with any of my 2 windows pcs and 2 windows laptops even though 2 of them are complety useless and out of date could be used easily as midi controlers etc, i have a 9 year old pc running xp very happily with no other upgrades, was origionally on win 98 so overall i think win is ok but i would prefer a mac.