Grimstonefire:
Which do you find the most interesting and why? Doesn’t have to be one that you own (or have any intention of buying).
Warhammerman:
Probably the Dark Angels or Blood Angels since they are so secretive. I mean the Blood Angels are plagued bt a curse that only those within the chapter and a few allies know of. And the Dark Angels are constantly trying to hunt down the Fallen and they will do anything to capture one. They are so dedicated to their mission that they have been known to leave battlefields and innocents all in the name of redemption.
Another interesting one is the Alpha Legion who fought for Horus during the Heresy for either personal gain or to permanently destroy chaos and save the world forever even though they would be destroying it. Can’t get much awesomer than that and the Alpha Legion are constantly duping Imperial Forces with Splinter Cells of Agents and all kinds of cool stuff like that.
Ishkur Cinderhat:
I have an affinity for the Imperial Fists, mainly since one of their own Lexandro D’Arquebus played a vital role in the “Inquisition War” novels which gave me the first (and hence most important) impression of the 40k Universe. I also think that their paint scheme, if executed well and with lots of battle damage, is one of the most striking ones on the battlefields.
Fluffwise, the Thousand Sons rock and I am absolutely sure that the upcoming BL novel will make them one of the most interesting legions ever (much like “Legion” did for the Alpha Legion, IMO). 
Willmark:
If I were to do a new SM army I would do a dark angels army, but make them focused on the Fallen, basically right after the HH.
Basically a themed force with few if any vehicles.
I normally go for the good guy route but these have a compelling story to me.
Thommy H:
Dark Angels. Obviously.
cornixt:
I didn’t realise so many people like DA. They were my favourites from the beginning, although the painting schemes GW use now aren’t as nice as they used to be. I’ve contemplated having both a DA army and an army of the fallen but I’ve never gotten into 40k enough.
Kloofpumph:
Whilst I do play a ksons army, my favourite legion is the word bearers. Demons, crazy zealots, and chaos Chaplains? Yes please :).
Thorne:
The Legion of the Damned are a mysterious band of Space Marines, probably the remnants of the destroyed Fire Hawks chapter, who appear unexpectedly from nowhere to help Imperial forces in times of great need. Indeed the best chapter ever to kick butt skulls fire brimstone and pure emotionless killing machines. What else would you need ?
Kloofpumph:
Oh, Legion of the Damned. Forgot about them.
Thorne:
Oh, Legion of the Damned. Forgot about them.x.x HOW !!!! x.x Impossible ! you couldn't ? Legion of the damned ? The best space marine chapter ever ? ... Well ... Pfft
Kloofpumph
Kloofpumph:
Urm…well…you see…They’re just so mysterious even I believed they were only a myth!
Yeah, that’ll work ;P…
Forgefire:
I would have to say Alpha Legion. Its an enticing thought that they are still loyal to the imperium (well atleast some).
GRNDL:
Its a trick question. There are no interesting space marine chapters.
Hashut’s Blessing:
GRNDL: Oh too true 
IMO, Iron Warriors 
I know that they’re a traitor legion and whatnot, but the Chaos ones are far more interesting. I hate the new Chaos Codex, but the old one allowed you to field armies that were actually different and played differently, rather than having different colour schemes, self-imposed weapon themes and the odd chapter that has its own book, that’s actually not all that different (from my experience,which is little).
Swissdictator:
With what little I know?
In the 41st Millenium… the Salamanders strike me as kinda cool. There’s one that their armor looks like steel… those look cool too.
In the history of the universe? Pre-heresy Luna Wolve’s.
Edit: If I can include Chaos? Either the Black Legion or Plague Marines.
Loki:
It would have to be legion of the dammed or Space Wolves as there is no where near enough back ground about the legion and the space wolves are just cool and they have the secret of the 13th company
speedygogo:
I like both the space wolves and the blood angels but dark angels and grey knights are cool too. My vote for the lamest chapter is the Ultramarines. I wish GW had kept the crimson fists as their poster boys for Codex chapters.
Hashut’s Blessing:
Swiss, I agree that the Salamanders seem pretty cool. In terms of colour scheme.
What I find odd is that they are all black (African/African-American, etc etc), whereas no other SM chapter is (which, whilst is fitting to people’s painting norm, is actually backed up by the fact that they are all, ultimately, sons of the white Emperor) and I have never seen an explanation. However, they only have ONE favoured weapon to my knowledge: any kind of flamer (they are cool), but it seems lacking in anything for tank-killing and range etc…
Thommy H:
They’re not “black” - they have actual jet-black skin and red eyes because of the interaction between the radiation of their homeworld’s sun and their gene-seed. It’s supposed to be clever how they look like monsters yet they’re the most humanitarian Chapter.
That’s relatively new though, and actually it’s pretty racist. See, back when the Salamanders were first given a proper identity during 3rd Edition, the 'Eavy Metal team tended to paint them black (as in African). There were still white guys, but there was a higher than usual proportion of black guys around too. It was just a little thing they did to differentiate them. Then, people latched onto “Salamanders are black” (as if no other Chapter should have members of different human racial groups…) and eventually it became canon, but in the really weird way described above. So, now, we’re actually back to all Marines (and pretty much everyone else in 40K) being white, and the only sign of any other skin tone is because of some kind of crazy sci-fi reason. There’s a reason I paint a few of my Dark Angels black…
Also, The Emperor wasn’t white - he was born in medieval Turkey, so he’d be Ottoman or something.
Hashut’s Blessing:
Thommy H, MOST informative, thank you very much ^^ Always glad to learn something. I am more inclined to be okay with their literally black skin in that case (despite their reasoning for coming up with it).
As for the Emperor, he was, yet he is still depicted as Caucasian (at least on the Horus versus Emperor picture on my wall, lol), which is why I was saying it.