Bracket Style:
Play 5 games and get placed in a bracket (bronze, silver, gold, platinum, diamond) based on performance in the 5 games played. You can move up and down in the bracket, and you can be demoted or promoted to other brackets based on K/D and Win/Loss ratios. This has been implemented in Starcraft 2 and Call of Duty: Black Ops 2 with great success in both.
Halo 2-style ranking system:
Rank based on a number from 1-50 that is determined purely based on Win/Loss ratio in games and not determined by K/D. You can lose and gain your rank. In Halo 2, this was a very clear indicator of how good someone actually was at the game. I recall being able to at least pinpoint someone's ability at that game based on their level.
****I personally would prefer the Bracket-style ranking system because I believe it to be the better indicator of skill since it takes into account K/D and W/L.
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That has to be a horrible idea. There is way to much cheating and glitching in pvp atm. Go to destiny tracker of your that concerned. Stop trying to make this a cod clone.