Any engine that looks like it actually gets used. If someone pops the hood and shows me a dirty looking small or big block with some bolt on mods and enough dirt, grease, oil and water stains to show that it actually gets driven then I'm impressed.
Yeah sure some giant hemi, or supercharger, tunnel ram, giant turbo or whatever is cool to look at once or twice. But all that perfectly polished, high dollar speed equipment tells me is that the car spends more time parked in a garage than it does on the road. Sure, it LOOKS fast. Heck it probably is fast. But it never GOES fast, so who cares? Just some rich guys life-sized car model at that point, sits on a shelf 99% of the time and occasionally gets dragged out to remind people how "cool" it's owner is for paying someone else to build it. Boring.