^Subject:.*xyz or SUB ?? xyz

Assume that the content of a header (for the sake of example,
Subject) has been saved in the variable (again for example,
SUB) as follows:

     :0
     * ^Subject:[       ]+\/[^  ].*
     { SUB=$MATCH }

What reasons might there be to prefer one over the other of the
following alternative recipes?

     :0:  # Alternative construction 1
     * ^Subject:.*xyz
     fileit

     :0:  # Alternative construction 2
     * SUB ?? xyz
     fileit

Would the answer be different for the following alternatives?

     :0: # Alternative construction 3
     * ^Subject:[       ]+xyz$
     fileit

     :0: # Alternative construction 4
     * SUB ?? ^^xyz^^
     fileit

-- 
Rik Kabel                                                 
rik(_at_)netcom(_dot_)com