The Toyota 1.6 liter DOHC 4-cylinder..had 1 in a 1991 Corolla. Reliable, smooth, powerful enough for what I needed...
Mazda 1.6 SOHC from the 1990-1994 323's...learned to drive on one, and then had one in another 323 for 3 years...took an amazing amount of abuse, and never complained...
I've never owned one, but I've always thought GM's 2.8 liter V-6 of the 1980's was a great engine - reliable, sounds good under acceleration, decent performance in the J-bodies (Cavalier Z-24).
I also like the 2.2 OHV 4 in my Cavalier - nothing fancy, but rugged and reliable....