Go with the A2403 all day long. A2K may break in easier but isn't always desirable; the A2000 series mitts/gloves have proven themselves to be pretty good at every level. Don't confuse marketing and paid MLB endorsements with quality.
CollegeParent, my son got the 31.5" at a garage sale for $10 basically brand new (I even paid him back on that one); loved the pocket design and the mitt. Now has a 34" he'll use with the junkball picthers in HS; used it this summer exclusively on his summer team to finally get it broken in for HS. 34" is a big mitt but he has the huge hands to handle it easily. Other mitt he uses in HS is a 32" Kelley Proline; great mitt for the money with a shallow/medium pocket.