Just about any BMW factory motor, S38B38, S14 2.4, S54B32, S65/85 including the Mclaren F1 BMW motor which is literally two 3.0l M3 motors hooked together with 12 itb's. In my own opinion in terms of logevity and badassness BMW builds the best motors out of the factory

If I could take anything it would probably be an E46 M3 with an S65 V8. 8500rpm, carbon airbox, lighter than the i6 and it sits farther back in the car. With a Motec and bolt on's they do mid 400's and it'll last forever. Without a doubt, it would be a beastly set up