In my neck of the woods, it seems like the Citadel Weapons Master is the go-to Daqan champion. Being a Waiqar player, I never gave it much thought until I started tinkering with Daqan lists in part to make suggestions helpful to my Daqan opponents. But now that I'm messing around with Daqan lists in earnest, it seems to me that Lancecorporal is a much superior choice, especially if you're running Hawthorne and doing a first turn inspiration boost.
Assuming Aggressive Cornicen, because that also seems to be a Daqan "must have" you get a guaranteed hit on the charge if you want it, which to me seems better than the possibility of 5/8 chance of a hit plus a 1/8 chance of a double hit. But the real treats are that you can add a hit modifier at the initiative 3 yellow attack action or add defense to an attack. You also get a small, but significant point savings over the weapons master... plus one additional defense.
The best case I can make for the Weapons Master is that since he doesn't exhaust, you can get more bang for the buck without needing to burn inspiration and rallies, for example if you're not running Hawthorne or don't have a rallying Cornicen handy. You can run Tempered Steel more easily because you're not competing with an exhausting champion for precious inspiration and rallies. And if you run him in 9-tray unit, then the defensive advantages of the Lancecorporal aren't as significant... although now you're playing with a very large unit that is already sucking up a lot of points and you've committed to a strategy of letting a fair number of that valuable unit die.
Anyway, my sense is leading me to think that Lancecoporal in 4 to 6 tray units of spearmen is more optimal. But what says the collective intelligence of the forums?