I'm not a guitar teacher - but a learner. After some mucking about with a pick I learned from Leavitt's Modern Method. That was very strict about down strokes for crotchets, then running quavers are down up down up. The quaver on the beat gets a down and the off-beat quaver gets an up. So a quaver pick-up is an up. There are various solutions for triplets. It did wonders for my picking. They have these picking etudes that are marathons to get through, but they are really good. The value in the system was it made you consistent, and accurate about placement of the arm and hand (where to I need to be to approach this string from this angle, and where will I end up? If I do a rest stroke will I mute the next string, is that what I want, etc, etc?)
Right or wrong, it was a system and now I can pick up a guitar and I will always pick like this and I'm fairly accurate.
Classical - Here I got very very confused. I felt the books were asking me to alternate i and m for no reason other than to confuse me, and to instill in me that this was the correct pattern, where in fact I have 5 fingers on that hand and there is no reason to neglect any of them. I had occasional lessons and found my teacher equally inconsistent. What he did say was that different guitar authorities have different ideas on this. At one point, he said that m would make a naturally stronger tone (longer finger) so I should use that for the on-beat quavers, i for the off-beats. Sometimes he would have me alternating i and m, sometimes p and i (which worked well as it felt to me like the down-up from Modern Method). Then arpeggios were generally pima.
I could never work out if I was doing something because it was easier to make it sound musical, or if I was doing something precisely because it was more difficult and mastering it would make me a better player. I'm a pianist, and I have this obsession with 'any finger should be able to do anything'.
I never really got the hang of fingerstyle on steel-string, but I have a funny feeling that if I had stuck at classical, then I would just finger things in a classical way.
I'm interested in hearing what others have to say, as it is in my mind to return to classical guitar at some point.