As a zerg against a bioball, should you focus fire on the medivacs, or on the offensive units?

Assuming it's early-mid-game and I have relatively few hydralisks and mutalisks behind my main force of zerglings and banelings, does it make sense to focus fire on the medivacs or just try to take out more of the things that can shoot back? Marines are appealing targets, given their high DPS-to-HP ratio.

If the answer is "no, don't focus on the medivacs," then based on this more general thread it sounds like there's no point on focus-firing at all, let units pick their own targets.

If it matters, I'm playing against the AI on very hard. I'm too chicken to try placing yet.

Seeing as you have few hydras and few mutas, but apparently a sizeable force of banelings and zerglings, I would say YES have your few units that are capable focus the medivacs AFTER battle has begun if possible. Your going to want the marines busy with the banelings and zerglings so they wont pick off the few mutas and hydras you have. Micro a bit, force the medivacs out of position and pick them off. Really however, if your Bane\Zergling force is appropriatly sized, the medivacs shouldn't help the Terran player much. Banelings pretty much instakill marines.

I wouldn't recommend caring too much about the medivacs in a straight on main-army (pure bio) fight.

If your enemy has pretty much only marines and maybe a few marauders, it's much more important to make sure your banelings connect properly with the bio ball - and other things like microing overseers to avoid widow mines.

Most times, your banelings decimate the bio ball or they take too many good hits from widow mines. Either way, it will be over pretty quick, so it does not make much sense to try and focus the medivacs.