Loooking back, I regret not buying the Marvel Western reprint series and Sgt.Fury. I missed the All-New X-Men and Miller's Daredevil which weren't titles I bought then. For DC, I ignored most of their war books, except for the occasional Unknown Soldier.
What's your collecting regret?
I regret getting rid of my Chris Claremont/Dave Cockrum and Cockrum/John Bryne-era Uncanny X-Men issues.
I missed the first story arcs of "Fables" and "Y-The Last Man" though I got the trades. I wish I had more of the 70s "Jonah Hex" and "Weird Western Comics". I read the "Marvel Zombies" trades. I got the fourth series only because of the horror characters but it's just too silly now.