I've got a Fat Guys Free-style 1/16th, and have used 4mm and 5mm. I'm a fan of the 5mm even though they're disproportionately larger than what they'd realistically be on a baitfish that size. That said....99.9% of my fishing is done with a round head 1/32

Not a fan of the reptile eyes either. My hands aren't steady enough to stick them with proper pupil orientation lol