New units. Their discussion and selection of upgrades.

It depends on who you're playing against! For example, against Inferno, they can really cause some trouble! And yes, they do die quickly, but now that there's a new tier of units, people are focusing on them to prevent them from spreading. But many people overlook the old tier, so sometimes they manage to reach their target! And then they cause havoc!

P.S. You shouldn't use them against every opponent! And while the new tier might be better than the old one, you shouldn't forget about the old tier either! IMHO.