For an Army retiree, What crest (DUI) is worn in flash of beret?

Here's the DA PAM's piece on it. Emphasis on paragraph b.

21–24. Insignia representing regimental affiliation

a. Authorization. AR 670–1 authorizes insignia used to represent regimental affiliation to consist of either the RDI
or DUI. A Soldier’s Regimental affiliation using an RDI is based on a Soldier’s branch/corps/special branch as
determined by PMOS or specialty. A Soldier’s Regimental affiliation using a DUI is based on a unit in which the
Soldier is serving or previously successfully served. Soldiers may wear the RDI for their affiliated regiment or may be approved to wear the DUI for a unit in which they are serving or previously successfully served.

b. Approval Process. Soldiers who desire to wear a DUI (in lieu of an RDI) to represent their regimental affiliation
must make the request using a DA Form 4187 (Personnel Action). A Soldier’s unit personnel office must verify the
Soldier’s assignment history to verify eligibility before changing the Soldier’s records.

c. How worn. The RDI or DUI, when worn as insignia to represent regimental affiliation,

I see that this question is still out there hanging after more than seven years! I have been wondering this myself for a while, not for wear on a beret or garrison cap, but for my AGSU coat. I think the response by CPL(P) (Anonymous) below is off-target, because it's dealing with regimental affiliation and the authorized insignia to be worn if a Soldier wants to affiliate with a regiment other than that of the Soldier's current MOS.
Based on some other language in 670-1 regarding wear of a DUI by Soldiers assigned to a unit without one, it appears that the RDI may be worn instead - this is probably most appropriate. However, a miniature (lapel pin sized) Retired ID Badge would also be very appropriate in lieu of a DUI, as would a US Army logo pin...
Honestly, I'd say wearing the DUI of your last (or favorite?) unit is hard to argue against!