The SE and Mercier are the same bike, probably built at the same Taiwanese facility, set up with the same CRAP components, BUT, they are still a good deal.
The Charge is set up with nice components, but is plain gage (not butted) tubing, so it could be on the heavy side. For your first fixie I wouldn't worry about weight, so this might be the best choice.
The Steamroller is the nicest of this group. They are on the heavy side, so you won't be racing on it, but they are well built, and made for the street.
Personally, I encourage newbs to do what I did. Get an old road bike for $15 at a garage sale. Buy the cheapest wheelset you can find, and make a conversion. Only buy parts that you absolutely need to get it on the road. Ride it for about a year until you become a good, strong fixed rider, then move up to a nicer ride. You will become comfortable on the conversion not realize how bad it sux until you get a proper track bike. Once you make that change, it is like a breath of fresh air, a new machine.