Remove the sisters? No nuns with guns? How can you not love that? ^_^
If any codex has to go, it's one of the numerous Marine ones. There's just too many of them. I'd get rid of the Dark Angels, since they're the least unique, and instead introduce a Dark Angels HQ that changes the rules of your army, as the Vanilla Marine HQs do, perhaps to allow Terminators to be troops, and all deep strike in on turn 1.
Second choice would be Chaos Daemons. I love the daemons, but I'd much rather have them grouped in with the Chaos Marines, in a single codex.
The first casualty of war is neither innocence nor truth.
The first casualty of war is always subtlety.