This really is the first decision to be made when thinking about a new lawn and there are a variety of factors to consider.
Did you know that contrary to popular belief, grass seed does not necessarily make a better quality lawn than turf. The results can be very similar but the choices of grass type are generally far greater with seed allowing you to have exactly the right type of grass for your needs.
Seed sheets are an alternative seeding method. They can be expensive and require careful installation but once in situ work very well. They are particularly worthy of consideration for steep slopes where seed may wash away.