I'm going with "Other" because I can't decide whether the best (for me) is a soapbar, or a piezo. Or both!
Right now I own two fretless basses: A Rob Allen MB-2 with the piezo bridge, and a Warmoth with a single Bartolini soapbar (Actually ist's a quad-coil humbucker in a MusicMan-sized shell, so I don't know what to call it. But I'm sticking with "soapbar".) Those two basses compliment one another wonderfully, as each excels at doing exactly what the other doesn't do well. And if I could only own one fretless bass I think I'd go for an F Bass AC-6, which has both a piezo bridge and a soapbar.
So, yeah... Both.
Right now I own two fretless basses: A Rob Allen MB-2 with the piezo bridge, and a Warmoth with a single Bartolini soapbar (Actually ist's a quad-coil humbucker in a MusicMan-sized shell, so I don't know what to call it. But I'm sticking with "soapbar".) Those two basses compliment one another wonderfully, as each excels at doing exactly what the other doesn't do well. And if I could only own one fretless bass I think I'd go for an F Bass AC-6, which has both a piezo bridge and a soapbar.
So, yeah... Both.