Why? (noobs do) (which means I'm more of a noob cuz I can't counter them ) Still, why?
Either way, most Zergs aim for sling/bling/muta. Pretty mobile, so, good for harass. Slings+blings are great against marine forces due to how cost-efficient banes can be against groups of marines. If you've ever lost a lot of marines to a bane or two, trust me, you'll know what I mean XD