I kinda prefer buffalo worms. They grow to a maximum of about 1cm and are pretty much the same as mealworms. Advantages for either are that they're so much easier to handle than crix of FFs- and by the time they've outgrown them, you can put them straight onto decent sized crix - cos i hate the micros :x
Buffalo worms appear to have a slightly softer exoskeleton to mealworms and you can tell that for the first few seconds or so the mantis is just trying to find a ***** in the armour. If it gives up, just crush the mealworm a little and feed it manually.