Since we are talking about SM chapters, how about helping me choose one. First the limitations. I don't want to do "the usual" chapters, which pretty much includes most of the first founders. So ruled out are:Blood Angels, Dark Angels, Imperial Fists, Ultramarines Salamanders and Space Wolves. I also want to use all of the troop types which kind of narrows it down to Codex chapters. Out go White Scars, Iron Hands and Black Templars.
What I have personally considered.
1) Raven Guard. Pros: Interesting fluff, uncommon. Cons: dull (if easy) color scheme.
2) Angels of Vengeance. Pros: Dark Angels organisation, uncommon. Cons: dull (if easy) color scheme.
3) Celestial Lions. Pros: Interesting color scheme, uncommon, don't like Inquisition. Cons: according to fluff were about destroyed, difficult color scheme (how do I get that golden yellow?)
4) Death Knights. Pros: I like the shade of their green armor! I get to invent my own fluff. Cons: I must invent my own fluff.
5) Mortifactors. Pros: Nice fluff (see the second novel about captain invictus). Cons: laborious to paint in epic scale.
6) Novamarines. Pros: nice color scheme (the old one from RT era, NOT the one in new GW fluff). Cons: laborious to paint in epic scale.
I have Epic UM, BA, SW, DA & Salamander SM Regiments ... 
If you don't already have other armies (or even if you do) try to choose a colour which will contrast to them (or what you are planning to paint them when/if you get around to it). My orks are many green/red, and I am planning on building a valhallen IG army, so Imperial Fists would stand out from both of them. Actually Imperial Fists would stand out from anything. 
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