Depends on the song/style/sound needed.
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Depends on the song/style/sound needed.

A lot of this.

I spend most of my time playing big riffs or black metal, so for me, fretless would just make life harder. Every time I've ever played a fretless I've had a lot of fun, but for me, for now, it's more of a toy than something I can really use effectively.

If you played a lot of jazz or something, I can see why you would want one. That smooth fretless/flatwounds tone is a sexy thing.
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Depends on the song/style/sound needed.

Obviously but for the genre of music you play most, which one would it be?
I own both but I use my fretted more currently. However don't get in the mindset that fretless is genre specific to jazz. Mick Karn of the band, Japan, made great use of its sound, as did Franz Kellner of Strange Boutique. And let us not forget Les Claypool, who proved yes, my bass friends, you can do all sorts of things with a fretless including slap. And Gary Tallent (Springsteen) has used one in straight ahead rock.

And the first fretless was developed by none other than Bill Wyman of the Rolling Stones

Fretless does take extra work to become proficient at playing. It can be rather unforgiving in the intonation department. But if you want to add that sound to your arsenal, it's well worth the effort
I play fretted most often, but for expressiveness nothing beats fretless.