It should be played with pull offs one the e-string , and alternate the b-string .

e-17p12----------12-17p12----------12-17p12----------12-15p12---------
b-------13-12-13----------13-12-13----------13-12-13----------13-12-13-


However you can alternate it through out like the pattern at the end of michael angelo's speed kills . (start with a downstroke)

e-15-12-----------12--
b--------13-12-13----%



The way that sounds better (or easier ;) ) to you , is the right way.