Could be a couple of things. If the pads in the caliper with the high wear aren't worn evenly then you might need to lube and/or replace the guides pins because the caliper isn't sliding freely. If the pads in the caliper with low wear are worn evenly then you could have a flow blockage or a stuck piston in the caliper.

On my car under braking I noticed it would pull to the right. Upon inspecting the brake I found the right front brake pads worn a lot more then the drivers side. Odds are you have a caliper that is sticking. Rebuilt kits are available to fix it. Make sure you check the brake lines too to make sure their not obstructed as that can cause the same issue.