As long as they meet the 12" minimum, I would go for expansion. HST fails the 12" in steel, but both meet 12" or more in the other areas. Personally I use HST as it is better in bare gel and heavy clothing. If I ever get into a gunfight, I think it is unlikely I'd be shooting through car doors so I'm willing to sacrifice a little performance there (ie. if 90% of the time clothing is all you worry about, go with what works best 90% of the time). I think most muggers are either going to get shot right away or they are going to run like hell when the shooting starts, unlikely they will take cover and shoot it out with you
Edit: you mention duty. If I was in law enforcement I would consider the barriers a little more, but would still think the HST is the best all around performer.