So today's top 3 will be the top 3 hardest to kill units. These units will be selected for their complete resilience to small arms, and sometimes, ordinance fire. This category is non-HQ.
1. Chaos Plague Marines
These guys are 1st, no competition. For a measly 23 points, you get Toughness 5, a 3+ armor save, defensive grenades, and Feel no Pain. I have
seen these guys face down a charge from Ghazghkull Thraka, a bunch of Nobz, and a Warboss, and stay alive for 6 rounds of combat, while causing a pleasing amount of casualties. They are also nearly impervious to small-arms fire, and when entrenched in cover, it will take a heck of a lot to get them out, what with defensive grenades.
2. Chaos Demons Plaguebearers
Coming in second, these are pretty much Deepstriking Plague Marines, except for 8 points cheaper, with no power armor, and an invulnerable save. And some statistic changes. Okay, so not much like Plague Marines at all. Okay, well, they are a really good screening unit, being cheap enough to be disposable, except for that they won't die very easily. Overall, a very nice unit.
3. Imperial Guard Ogryn
A little pricey per model, but you still get some pretty good stuff with these guys, what with toughness 5 and 3 wounds. Take it from me, it takes some effort to kill these big dudes. They are a little more offensive than most unkillable units, with Furious Charge and those big guns that I can't remember the name of.