I've tried big transports a few times with mixed results. In the average pick-up game style skirmish they sucked. They're too slow at deploying your infantry in force, and they have to spend several turns loitering in high priority areas where they will be targeted. Even the "give them a better target" plan doesn't help when you put that big a target on a relatively fragile vehicle. It just doesn't do enough versus taking multiple transports and rushing.
But in a few games played on water heavy maps with marshes and islands, the ability to drop single BA Squads/foot platoons in the only cover proved potent. A single Maxim II and a company of foot infantry can quickly contest all the most important area and position spotters, all for less BV than most light 'mechs. And with all the water slowing down movement, the limitation on deployment was less problematic than the ability to move over water was an advantage. Battle Armor proved even better thanks to the combination of movement and firepower, but the BV ratio was less favorable. The same tactic could have been done with multiple smaller transports, but the BV difference was worth the attempt.
In short, I generally found big transports to be less useful than multiple small ones except in scenarios where I had a significant advantage in movement and/or positioning from the start.
