On account of my quite limited experience, I don't think I can come up with three favourite engines. Rover V8s - no. A very smooth, free reving small V8 of 3.5 liters, but it did have a weakness with main bearing issues (after high mileage), shifting liners (on one engine) and two broken crankshafts. Also susceptible to wear in valve gear - the rocker shaft.
Rover six cylinder 3 litre - no, whilst lovely engine, side tappets difficult to adjust, also inclined to burn exhaust valves.
Mercedes M100 engine - 6.9 litre only. Probably my favourite on account of longevity and robustness, and excellent torque. The 'hold steady accelerator' is remarkable as the revs approach the torque range of 2500-3000 rpm. Start off with 2K. revs, hold accelerator steady and watch the revs rise and the speed build up as the tacho needle creeps upwards. You don't even have to press the accelerator. Also, like oil capacity and dry sump lube system.
Chevy Gen 3 5.7 litre engine - lots of silky smooth power, quite economical and just about whisper quiet.
Last but not least - Valiant 6 cylinder hemi engine - wonderful power from 4 litres (?) and utterly reliable. I guess that's about the extent of my experience. Regards Styria