As a rule, I don't want a lot of examples by the same artist though I will buy multiples for various reason, e.g., different characters.
(1) On which artist have you spent the most money to date?
Yale Stewart - That's driven by a single commission that is the most expensive piece in my collection.
H.G. Peter - if you are looking for published pieces
(2) In your collection, which artist's works have the most combined value (when assessed objectively)?
So many of mine are commissions (sell at 50 cents on the dollar), it's really hard to say, but if I had to guess, I'd saw the Curt Swan pieces are the most valuable as a group (2 commissions - Superman & LSH - and 2 published pages (LSH). Again, this is biased because I have so few per artist - an average of just under 1.5 per artist.
(3) In your collection, which artist's works are the most common?
As mentioned, I average just under 1.5 pieces per artist.
Yale Stewart - 9 pieces followed by Joe Eisma and Thom Zahler with 5 each, Curt Swan, Nick Pitarra, and Terry Moore with 4 each.
This is just my collection, if I were to throw in my wife's and my daughters', Katie Cook with have the most pieces of art (27). Those mini-paintings are addictive!