Did a quick cursory test against arcane oozes. Base weapon damage lands full with orange numbers but the extra typed damage (true law, screaming) shows yellow dr numbers. It's weird.

They were also unsurprisingly immune to holy and anarchic. Those four (holy, anarchic, true law, screaming) happened to be the only special damages I had on me at the time. I whipped up a True Chaos shard to test with my paladin; I'm curious to confirm that there is no umd check or negative level when wielding opposite-aligned True Alignment weapons.

Based on that test, True Law and Screaming are identical for oozes and rust monsters, so I'd go with Screaming because they look cooler and air essences are easier to work with than law essences. (You can convert air lessers to greaters by deconing low level shards, but laws have no 0 greater 4 lesser recipes to do that with.)