It's mainly on what you want the car for and how much power you are looking for. Which head you use and how well it is built up has a lot of role play in making big power with the l28et motor. With a big turbo you will have quite a bit of lag using a 12 valve head .. so you need a head that is going to rev out and be able to make that big power with a large compressor. The info above is all correct, T3/T4's are the most commonly used. Just put more information up and I can give you some idea.