It depends how percussive you want your slap & tap to be, i have to use two basses as the fretless bass doesen't sound snappy enough for that style to me, Having said that, a Wal custom fretless will do both very well, When you pull up on the volume contol it engages a pick attack & almost makes it sound as though it has frets (great slap sound even when fretless) but they are very expensive,
Playing fretless in a rock band? I do & it sounds awsome!
Check this guy out,
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