I bought the late 2008 first unibody macbook pro. for the price you getting it, go for the 15.
It has express card, you can change the battery and hard drive easily without opening the interior of the machine.
You get the dedicated 9600m gt whenever you need it.
the 15 inch is more beautiful, that's my opinion.
after almost 2 years owning the machine, it makes people go WooW when the see it.
you will not have the 10 hours battery life but you can buy another battery change it on the go easily.
plus it has applecare 2/12.