Death Company pair a Veteran statline with Rage and Feel No Pain for a decent point cost. They’ve got Relentless too, if you really want to arm them all with bolters and rapid fire before assaulting (I usually pair bolters with power fists and thunder hammers for the extra shot; there’s no downside). Any Death Company Marine can take power weapons, power fists, thunder hammers, and hand flamers, inferno pistols, or plasma pistols. The squad can take the standard Dedicated Transports, but I prefer jump packs as they will generally get them into assault faster. Even so, a large squad of Death Company in a Drop Pod landing Turn 1 would be something the enemy would absolutely have to deal with.
I find that Death Company work really well with minimal upgrades. With so many attacks on the charge, they don’t really need power weapons. I generally take one power fist per five marines to allow them to deal with hard targets and leave it at that. If you do have the extra points for a power sword, it will do some serious damage, but it’s not essential.
One of the big advantages I see for the Death Company is that they perform well in small squads. Our other assault units really benefit from a Priest for Feel No Pain; since Priests are a limiting factor, it makes sense to pair them with large units to get the most out of their buffs. On a similar note, large Sanguinary Guard units are more efficient due to the Chapter banner. However, Death Company have no such limitations. Many small squads of them are perfectly viable and very threatening. If you’re looking for an MSU build (as I am lately), Death Company are your best assault unit.
Lemartes, Guardian of the Lost
Lemartes now takes up a separate Elite slot rather than being an upgrade to the Death Company, though they are still the only unit he can join. Lemartes has the statline of a normal Chaplain, but gains a master-crafted Crozius Arcanum, Feel No Pain, and Rage. He also gets an extra attack and point of Strength when he loses his first wound. Altogether, not bad for the 25 points he costs beyond a normal Chaplain with a jump pack.
If you want a Chaplain to lead your Death Company but don’t want to spring for Astorath (say because you’ve already used your HQ slots or aren’t taking a very large squad), Lemartes is a good choice. He’s more dangerous than the standard Chaplain, but limited to only leading Death Company. Consider him a mid-tier character, better than a Chaplain but not as good as Astorath, and you won’t go far wrong.