The two best turbos are pretty much down to the HX30W family or the HE221. Probably the HE221 may be the absolute fastest but the HX30W isn't far behind. Unless you live at high altitude like Steve, you want the 6cm turbine housing on the HX30W. I believe the HE221 may be a 7cm. On the compressor side of the HX30W, there are 3 choices. A 40 mm, 44 mm, and 46 mm (known as the Super HX30W). The 40 mm HX30W was the stock turbo on the P pump 4bt. The 44 mm is probably the best choice if you are considering doing twins and the Super HX30W is the best for max power with a single. All these have the T3 exhaust flange which will bolt right up to the stock manifold. The HE221 does everything well too. Spools super quick and builds good boost. It has the T25 flange which will require an adapter to the exhaust manifold. It's a little more difficult to clock if you need the outlets facing a different direction because the wastegate actuator is attached to the compressor housing. Also, the HE221 is less common in the market. Member Alcaid can help if you want a new one. He has the best prices on any of these that we know of. Beware of the cheap clones sold in the market. They aren't genuine Holset units.