Fun fact: 9/10 users with no linked gamertag are better than you at Halo. That doesn't necessarily mean that I am; but it does mean there's a pretty solid chance.
Posted by: Darkstar_81
W/L and Arena rank are more of an indicator of skill.
lolArena
Win/Loss can be padded just as easily as K/D. Search with a full team; even if your entire party is bad, if you communicate and make sure to grab your team's assets as soon as they spawn, you'll have a marked advantage over randoms, even if they're better than you.
Personally, I think headshot efficiency, individual playlist K/Ds and weapon-specific K/Ds are the best indicators of ability.