Nestled IF(NOT(ISBLANK)) Statement?

I would like to return column D based on Columns A,B,C as shown below

A     B     C     D
AA    BB    CC    AA
      BB    CC    BB

Basically, if there is something in A return A, if not return B, then finally C.

I used this equation on some test data and it was working for me, but when I applied to my actual data set it doesn't work properly. It's not working for values in columns B and C, it's just pulling in A and returning blanks for everything else. FYI A,B,C are all similar equations that return a "" when they can't find a match. I tried hardcoding B&C to troubleshoot but no dice.

=IF((NOT(ISBLANK(AE2))),AE2,(IF(NOT(ISBLANK(AF2)),AF2,AG2)))

Here's the formula that worked with my test data. I just c/p and changed references but it broke somewhere D;

=IF((NOT(ISBLANK(J12))),J12,(IF(NOT(ISBLANK(K12)),K12,L12)))

Any suggestions to simplify are welcome as well!