I enjoy a mix of units for functional overlap. Dreads are excellent and I admit I typically use leviathans and contemptors. Lots of cultists even with the nerfs they are essential for screening and board control.
Also a mix of oblits and las havocs. Chain
csm also usually make an appearance. Then multiple psykers always a
dp and at least one jump sorcerer. I also like mechanized zerks with exalted champ escorted by contemptors at move 9".
Lately I've been splashing into flawless host for the more fighty
hq's and possessed. Again semi competitive is what I prefer.
Death guard lack most of that and mobility and most of the better psych powers and their
fw options aren't any better
imo.. Leaving them with pts denial
pb bombs and no
los weapons via pbc. Plus morty and friends if you like that sort of thing. Again I feel dg is pretty limited.. if you want to keep with any real identity.
AL can take on many identities. The competitive dg builds are pretty well sorted out but not my bag. Do a Google you'll see what I'm talking about.
Edit- it's worth noting the pbc is more appealing in itc format. Otherwise it's more like a defiler that can't fight.