Go with unlimited. The 250mb won't be enough for any extended use in this manner. I would say you could easily stream 50mb an hour using Pandora or Youtube constantly, though I haven't had the occasion to test it for sure. However, I was just using pandora for about 25 minutes, and it looks like I used about 20mbs of data.
Bottom line when deciding on a plan, if you think you'll use 3G more than four days a month, go unlimited. If you plan to use it every day, even a little bit, go unlimited.