I see no reason to limit yourself to one technique.
I usually use three but not always, their are times with thumb index has the mojo I'm looking for (like palm muting).
Thumb middle is rarely used but has its place (harmonics).
Just because I use a pick in one part of a song doesn't mean I will use a pick for the whole song.
I think we should all practice different techniques from time to time.
You never know when tucking that pick up under your pinky and slapping that bass senseless is going to get you a gig but if you do not have that trick up your sleeve
how will you use it