Re: fingers or a pick??
I learned to fingerpick to apply this tecnique to acoustic guitar. Mainly slide, most of the slide players that I have seen and admire are compentent fingerpickers. Not to say that you can't play slide with a Pick. It is more difficult to mute the unwanted notes with a pick in your hand (IMO). Bottom line is the more ways of picking you have at your fingertips (no pun intended) the more choices you have when attacking the strings.
When I play Electric guitar, I always play with a flat pick, but I do have a tendency to cup it in my middle finger, and pick with my thumb,index, and ring when I need to. The one tecnique that I have never seemed comfortable with is Fingerpicks. I find it awkward not being able to feel the strings under my fingers. If I could play alternate picking with my fingers I would not use a pick at all.