Looking at the Hugo nominees for this year and cross referencing them with what was chosen for the 3 big year’s best anthologies we find:
No Hugo-nominated novellas were included. While there isn’t room to print all of them, usually a couple make the cut.
Two of the five Hugo-nominated novelettes were included
“Fade to White”, by Catherynne Valente – in the Strahan
“The Girl-Thing Who Went Out for Sushi” by Pat Cadigan – in the Dozois
All three of the Hugo-nominated short stories were included, all in the Strahan anthology.
So clearly Jonathan Strahan has his finger on the pulse of the zeitgeist, or something. I should point out that none of the 4 Grant/McGuire nominations made it into a year’s best. Draw your own conclusions there.
Meanwhile Amazon lists Hartwell’s Years Best 18 as being published on December 10, which seems a little late for covering 2012 and a little early for covering this year, so something is going on there. It’s jumped from Harper to Tor and from mass market to trade, so previous editions may become hard to find, brand new anyway.