Well, look at it like this...
Branch had two long TDs, weaving through traffic while Morgan was WIDE open on his two TDs (the one from Kevin Johnson was a fluke, IMNSHO).
Just imagine when Branch starts getting balls thrown at him when he's wide open; besides that, he's like one of the fastest guys in the league. You know Brady will keep throwing it his way until they start doubling him (not likely).
Go with Branch until Morgan proves that he's a playmaker like Branch.