I personally like the Dunlop Flow 2mm (for both guitar and bass) or the Dunlop TriStubby 3mm (for bass). Thick and rigid (so that the notes break precisely when you want and there's no slight fudge factor due to a pick bending instead of breaking through the string) and also with a nice fat rounded bevel so that your notes keep good bottom and don't get shrill (happens to me with sharp picks).
In this picture the TriStubby on the left, the Flow on the right, and the Flow JP (which is essentially a slightly smaller 2mm Flow with the DT logo, red color and no texture) in the middle - the JP I don't like for bass, only for guitar, I feel it slips away when I'm playing bass. The other two have much nicer textured grip so they stay in position easier when dealing with the bigger mass/reaction of the bass strings. The dime is for size reference.
In this picture the TriStubby on the left, the Flow on the right, and the Flow JP (which is essentially a slightly smaller 2mm Flow with the DT logo, red color and no texture) in the middle - the JP I don't like for bass, only for guitar, I feel it slips away when I'm playing bass. The other two have much nicer textured grip so they stay in position easier when dealing with the bigger mass/reaction of the bass strings. The dime is for size reference.