Basically, list your favorite military units in
40k and explain why you like them.
SM - Space Wolves - These guys are basically a definition of noble barbarian. First impression for most civilians would likely be "I gotta get the hell away from these guys"... and then they get to know them.
SM - Raven Guard - Same reasons as with Space Wolves, minus the "barbarian" thing - though they may actually be even scarier to average civilian than Space Wolves would be.
SM - Lamenters - What can I say? I'm a sucker for "I remain a decent guy despite all the gak universe throws at me" stories.
And this.
SM - Black Templars - Basically? Fell in love with them due to the Helsreach.
IG - Cadian Shock Troops (and Cadian Regiments in general) - OK, this one is likely in part due to exposure... they are
the prototypical
IG regiment. But I really like the fact that they don't really have any interesting quirks... just discipline, perserverence and faith in the Emperor.
IG - Valhallan Ice Warriors - CAIN! Also the fact that Valhallans are (in Ciaphais Cain books) portrayed as being both doggedly determined as well as rather pragmatic. Not sure how much of that is Cain's influence, but definitely something I liked.
IG - Tanith First And Only - They are basically Dunedain Rangers...
IN SPEHSS! So yeah.
IG - Praetorian Guard - Redcoats in Space.