Fingers.
I am not a fan of picks on either bass or guitar. Picks sound really plucky/scrapey/metallic to me, so i play guitar with my thumb. On the other hand, playing a bass with my thumb sounds very flabby and undefined to me, so i play with my fingers. I used to play with my thumb sometimes when i first started playing bass though, because it was a bit easier coming from guitar.
I am not into slapping. I used to like it when i first got into bass playing, but i grew out of it. I never could get the technique down anyways, and i play fretless exclusively now, which is the opposite sound.
Tapping is nearly impossible on fretless. :tard: Aside from maintaining intonation, the strings don't have the same "fret sound" to them when you tap them down.
I really love tapping on fretted basses/guitars though, but unfortunately, i am really bad at it, so i don't use the technique.
I love Steve Vai's tapping on "Building the Church". (The G3 version, not the synthesizer/digital crap he did on the album version)
I really wish i could do that!