Originally Posted by nyarlathotep
Cause to be honest zoanthropes and hive guard are pretty good at popping transports, but that means you don't get venomthropes.
Problem with Zoanthropes is their powers work like this;
PsyTest => Roll To Hit => Roll to Pen => Roll to damage
3 (or 4, if you don't like damage rolls) chances to fail. And that's not even including that every other army out there tries to shuts down Powers whenever they can. Compare to a Librarian Dreadnought with Lance. While it may have failed it's Psychic Test - or otherwise failed to kill a vehicle - it's still a Dreadnought with an S6 Force Weapon.
Hive Guard are great. But, AV13+ still is a problem. Like Predators, Leman Russes, and Ironclads with dual-Flamers that are about to tear your swarm a new one.
Of course, there are Tyrannofexes. But, they cost as much as a Land Raider (or Mephiston) and aren't anywhere near as good. Not to mention that they're apparently a pain in the butt to make - if you can find a conversion idea that you like.
Also sadly the FAQ has gotten rid of the best anti-mech Doom's ability to hit people inside transports.
Tyranids (or, rather, Malan'tai Lists) were incredibly good right up until that happened.