If you're playing against weak guards (Bobcat) it may make sense to attack with a level 1. Against a powerful guard like Iron Golem, my first choice is to neutralize them some other way, preferably with Tanglevine, but throwing your level 1 creatures under the bus is generally a poor choice. Tanglevine is a much better answer to corporeal guards, since they'll need to waste time killing the Tanglevine or use a Teleport to get out. Either way, it's better for you than throwing a Fox under the bus. Bobcats, on the other hand, may be a good choice due to their defense.
I wouldn't want to waste a Pet Steelclaw attack on breaking through a guard, but a Pet Timber Wolf or a non-Pet Steelclaw attack wouldn't bother me as much. Sure, losing them is much worse than losing a level 1, but it's also much less likely that they'll die. A level 1 will die on average from an Iron Golem attack. A Pet Timber Wolf will take ~3-4 attacks to die, and that's if you don't heal him at all. Of course, you could use things like Block/Reverse Attack/Sacred Ground/Fortified Position to make it less likely that you're level 1 will die, in which case it makes more sense to use them to trigger the guard. Timber Wolves are among the best creatures in a BM's arsenal for triggering guards. They're tough enough that it will usually take 2-3 attacks to kill them, even for powerful guards, they're attacks are relatively weak for their cost compared to Foxes and Falcons, and they're cheap enough that it's not terrible to lose them.
If there is a significant chance of losing a big creature to the counterstrike, or even if it's likely to result in the big creature being weak enough to be taken out with a zone attack, it's probably better to find another way to disable the guard. If the big creature is at full health, it's often better to have them trigger the guard so that you can get other attacks through from creatures that would likely die if they took the counterstrike.
It's all about trying to force my opponent to spend resources to deal with more of my threats, while avoiding situations where they have efficient answers like a zone attack that can kill my big creature and several Falcons. If they kill my big creature, I'm still fine so long as I have my swarm. If they kill my swarm, I'm still fine so long as I still have my big creature. I'm only screwed if they kill/neutralize all of my creatures.