Basilisk is the odd one out here. It is a continuation of pre-Servo Firefox ( Firefox before Rust ). It is not exactly a “new” engine.

Ladybird is probably the most exciting project as it is most likely to create a new independent browser suitable for daily use.

Servo was very exciting back when Mozilla was heavily invested in it. Sadly, it was long dormant. It really seems to be heating up again though so that is awesome.