I gotta say that I loved both Dynaheir and Branwen (and Shar-Teel, but not as much). But two deciding factors came into play when I was picking favorites:
1) Dynaheir has Minsc. Minsc rocks!
2) Dynaheir's banters/romance makes multiple references to the Wheel of Time books, which I like alot.
So I gotta go with Dyna!