So see what you can get for that extra $175. On NW you only need 12,500 miles to get a one-way ticket if you purchase the other half. However, you'll likely have to do that in 2009 because of the Delta/NW merger and not sure if that program will continue.

In general, I go with the cheapest unless what I get (miles or better seat or free upgrades) is worth the extra price or inconvienence. I'm firmly a believer that points and miles are more and more worthless and I'd save your cash...