I'm thinking that yelling back at them may not be the best response. To do so will probably give them what they wanted - a (lame) excuse to further engage you.
I'd give 'em full eye contact...& a smile, all while still ambling down the road. It gives them two things: A sign that you aren't ignoring their yelps; & something they don't expect. Also, & as a minor pleasure to me, most people who are trying to piss you off don't like such an adverse response to their taunts.
One more good reason not to hollar back - should you need to defend yourself at some point, anyone else in the vicinity hearing you call back to the aggressors would be able to testify that you did so, possibly coloring you as someone who wanted to provoke the attack.