When my wife and I built in Cranston a few years back, we seeded, for the reason that it was much less expensive. It grew in great, and was a real strong root too. I was super impressed with how well, and how fast, it grew in. If we were to re-do it today, we'd likely have to do the sod. We have to small children and a dog now, so we would need an instant lawn. Before, we had the time, so we seeded. We were very happy with the results. Depending on the seed, you should see grass in a couple weeks, and be mowing in about a month and a half or so. Strictly depending on the weather and how often you water it and what kind of sun it gets.
We had our sprinkler set up on a timer to run for 15 minutes about four times a day. Gotta keep the ground wet for seeding. Even more so than sodding. I also raked the seed in so that it was under some soil as opposed to sitting on top the whole time.
I guess it just depends on weather you need an instant lawn or not. I was very happy with the seeding and would do it again in a minute if we didn't need the instant lawn.