Another consideration: A quality 30ish pick is going to maintain it's status and it's enchantment FAR better than a QL 10 pick will, and a QL 1 pick will poof if you aren't very careful watching your pick's damage level.
So the most efficient method for mining skillgain would *probably* be to acquire a QL30-ish steel pick (steel is rumored to take takes 20% less damage and hold enchantments betterper action) with very high Circle of Cunning enchantment and jump on some high QL ores until you determine which types of ores give you the most hits between 1.01 and 39.99 QL, then find a horrible trash QL version of that ore and go to town mining it.
If your skilling pick is also your everyday use pick, then look around and experiment on different ores that you have access to, again looking for an ore type that you generate a lot of hits between 1.01 and 39.99 quality