best spacemarines chapter

what is the most skilled space marine chapter of war and what fictional comic/video game ect ground army can defeat them if any??

Most Space Marine Chapters specialize in an area.

Salamanders specialize in light infantry, mid range combat with overpowering weaponry while maintaining good martial skill (with some being very good). Salamanders have also had some of the most powerful Librarians of any Chapter I've read.

Black Templars seem to have an emphasis on melee skill more than most other Chapters.

Dark Angels in close range engagements with fast moving, hit-and-run, raid-like tactics. The Angels also

Ultramarines seem to have the greatest balance between on Chapters.

Space Wolves are melee freaks using less refined skill than the Templars but have more strength, ferocity, toughness, and relentlessness than most other Chapters. The Wolves of Fenris are, in my opinion, the best candidates for most dangerous melee Chapter.

Blood Angels are calm, strategic, and smart about combat. They back this up with great marksmanship and melee skill. Not as much as some other Chapters, but noteworthy among the grand bulk of all Chapters.

So, they all have areas of expertise that doesn't really make one Chapter any better than another. It's mostly a matter of individual Marines. There's also the fact that many Space Marine Chapters operate well below their maximum allowance of personnel due to constantly being in combat throughout the galaxy, always being outnumbered, and the few amount of recruits who actually make in through the selection process.

Hope that helps.

Edit: Many consider the most powerful Chapter to be the Grey Knights, since they are ALL Psykers and all extensively trained in melee and ranged combat (like all Space Marines). But mostly due to the fact they are all Psykers.

@granitesoldier: thank you lol that was very helpful, any thoughts on any other army's that could beat them that are not from wh40k?

@hailasmodeus: Depends. If you allow Librarians, I'd say no. Librarian Dak'ir from the Salamanders destroyed a space cruiser the size of a small moon with his power and tore a daemon prince part with his bare hands. Psykers can take out entire armies by themselves in some cases, but they tend to be VERY few in number (Salamanders had three that I can recall, at any given time...at least only 3 named ones of any note).