The best engine I can think of is probably the 5.7 Hemi my Jeep comes with. I’m probably biased because it’s the engine in my car.
I think its a simple V8 with modern technology on its heads, its a gym bro that actually gets good grades on precalc for the AP program. I know that a lot of people really like the Coyote and the LS, but I’ll go left-of-field, I like the FCA 5.7 engine for many reasons, out of all the things my jeep crapped out during seven years of usage, the engine was never one of them, it never asked more than for some oil changes now and then and some preventive maintenance. It sounds great, it picks up nicely, and its, again, simple.
Generally I prefer more complex engines, for instance I am absolutely taken by VWAG’s EA898 4.0 L tri-turbo engine, it is a VWAG engine so it does have those annoying plastic chain tensioners that last as much as Youtuber’s career, but then again, being careful about it could probably save it!
Talking about chains and timing: I am more of a fan of the Freevalve tech that Koenigsegg designed and I honestly see more use for an electronic setup than a mechanical one, when you add simplicity it only makes the engine better. It is still a system that has a lot of issues worth ironing out, but I honestly think that it’s the way to go for ICE engines, together with HCCI technology. I think some manufacturer is talking about mechanically actuated adaptive displacement (by way of changing the stroke of pistons, don’t ask me how) but I see the most improvement in going for electronic heads, especially now that more parameters can be added, its cheaper than ever, and its advantages are quite noticeable both in the fact that it’s easier to manufacture, and easier to tune (or modify the tune)