I really like the Deathmarks.
Only 1 shot each, but longer range, hits on 2+ (if didn't move), d2, ap2, and has precision (great for killing characters - and here in 10th there's all manner of bonuses characters give when leading units).
They have Deepstrike.
And they can shoot at things arriving from deepstrike.
Killing characters is not the only thing these guys do.
They will take a toll on just about anything you'd care to target with them.
Their
DS ability gives you the option of keeping them in reserve for a tiurn, seeing where they're needed (either for shooting or secondary objectives) & then placing them to accomplish that.
And in the event you place them in a far off corner to investigate signals etc? Then after they finish their range(
LoS permitting) allows them to still affect the game as they reposition.
How is any of that not usefull in most games you'll ever play?
Immortals get more shots (though 1d & ap1 & Lethal hits) & can reroll 1s to wound.
Their advantage is that they are a solid unit with the Battleline KW & thus you can have up to 6 units of them.