This thread doesn't just have to be just combustion automotive engines alone, it can be any engine I've always been a fan of Italian engineering, despite the fact that it may not be the most reliable at times. For my favorite petrol engine, it would have to be the legendary Alfa Romeo 3.0 24V V6. For my favorite diesel engine, it's the Scania V8, purely down the power and noise it creates.
Renault K4M 1.6 16V. One of the toughest engines out there. It can pass 700k kms without any problems.
When you make a V8 big enough, it is going to be loud and powerful. My choices: Toyota JZ- and UZ-series, Ford Modular V8, Honda K-Series, MB OM617, Rolls-Royce V8, Cummins ISB.
I'm a big fan of the Toyota 2GR V6. I've driven multiple versions in multiple different cars, and it's all been excellent. 3.5 liters, naturally aspirated, upwards of 300 horsepower. Especially entertaining in the new 2018 Camry XSE V6, with 301 horsepower.
The X25TD. My dad's Omega has this engine, and with 500k kilometres (or something like that), the car stills running perfectly. The engine was made by BMW.
Honda F20C, used in the S2000... this is probably the greatest N/A inline-4 ever made. 240 HP, and revving to 9000 RPM sounds like fun to me.
Buick 3800 V6, used in almost all GM cars from the mid 1980s until around 2005. I like them because they have good torque, sound nice, simple so easy to work on, and are extremely cheap to repair because parts are everywhere. They also occasionally had superchargers from the factory which made them decently powerful with a pulley swap.
Kind of typical, but I'm a big fan on the 13B... Anyway, of course the 2jz-gte (gte over ge) And then there is just about any Porsche engine. I think they are some of the best sounding engines out there.....
GM Z30DT. Not high power (180hp/400Nm) but is so smooth. Jaguar 3.0 Diesel V6 (latest gen, 300hp/700nm) fantastically powerful whilst sounding quite cool. RR 3.6 TDV8, (270hp/640nm) has buckets of torque, enough to send a 2.7 tonne Range Rover barreling down country roads without straining.