With the new 7 damage s4 and DB1 having a beter combo window, considering that worse damage scales should go later in the combo (and DB1 damage scale is still crap) I've found this 1 bar combo from EXDB4 that so far beats any EXDF1 combo that I can find, It also beats combos using EXDB4 after the launcher.
B1(or any non launching starter)EXDB4, JIP, 421, DB1, D1, 43, BF3 = 43 mid screen damage for 1 bar. Also 43 damage if you start with 421. The corner carry is otherwordly too.
Edit: B1 after the D1 at the end of the combo is easier to execute and only reduces total damage to 41. It also allows you to finish wih spinning blade instead of a tele-move. You sacrifice extra damage but spinning blade is a +22 HKD that finishes in range for another attack while your tele moves advantage is crappy.