I haven't owned a bass with humbuckers so I don't really have a clear opinion about that, but I love the single coil sound on my JB's.
On guitars, I nowadays prefer humbuckers over single coils. They have a much fatter tone that cuts through better (don't believe it's the high crisp that makes a sound cut through, it's the low mid-middle frequencies). I like to play jazz, but it just doesn't sound right to play it on my Strat. I need to get a Les Paul or something to get the right sound....
When I started out on guitar, I didn't like the humbucker sound because it sounded dull to me. I wanted that crispy single coil sound that was easy to play with, and bought a cheap mexican strat and later a thinline Tele. The latter I traded in when I bought my first bass, because I never felt the sound was "mine". It was just too thin sounding for me. I've been longing for a les paul for many years now, but as my main instrument has been bass the last 6 years, I haven't been wanting to spend money on that.
The SG sound is also great, but it's more suited for rock than jazz as it has a harder and more "direct" sound than an LP. So I wouldn't buy an SG, but it's just a matter of personal taste. If I played a lot of AC/DC, an SG would be a must-have.
