Overall I don't have one fav but here is my short list.(# means currently still own) #Toyota V6 in my 02 Sienna:Very smooth and wide powerband. Datsun/Nissan L28 I6 in a 83 280ZX:Very nice with good balance and darn TOUGH! Ford 2.5L Duratec in 95 Contour:Great engine.Very smooth and powerful. #BMW M10 2.0L 4cyl in my 79 320i:A classic Bimmer engine with great power and smoothness for a 4cyl.Loves to rev! List of some of my worst engine experiences.. Geo Metro with 3cyl engine(rental):the little engine that couldn't... VW 2.0L DOHC in 90' Passat:Quite rough and loved to overheat if it hit 70 degrees outside or if it just felt like it.