I have 3 to cover the whole car, a 3/8" drive, a 1/2" and a 3/4"
The 3/8" I tend to use for 90% of an engine build, it has a range from about 5 to 70 ft/lb, it does everything in an engine re-build except for the Cam Shaft Nut, Harmonic Damper Bolt and the Flywheel Bolt.
I have to say, I hardly touch the 1/2" drive wrench during an engine re-build.
The particular wrenches I have are all Warren and Brown. The two smaller ones are the 'clicker' type and the big one is a deflecting beam. The clicker types have an advantage where left and right hand threads are involved, however on our Minis, there is only one of these. Some of the deflecting beam types can also go both ways (turn them over). Given the choice again, I would go for deflecting beam on all of them. They are more accurate and better to work with.