I'm not sure about favorite but I like..
The LQ1. Someone hit 257 whp n/a with one of those.
The vq30 & vq35 engines. Those engines have alot of options when it comes to swapability. For instance, IIRC the vq30 has 3 upper intake manifold to choose from. 2 of which are variable. vq35'* have a few options as well. Not to mention you can mix, match and frankenstein the crap out of those engines.
The SHO Yamaha motors are pretty sweet and newer Beemer engines have me amazed.