If you demand the utmost in PQ (i.e., 24Hz video) and/or lossless audio, the ATV3 will be lacking. If you can live without those two things, I've found that the ATV3 (and ATV2 if you only need 720p) is capable of delivering very high quality video and 5.1 audio. *BUT*, for optimal quality, you really need to get your videos converted to MP4 format.
Well, let's say, your needs aren't even quite *that* high. OK, I can tell you that I've had very good results with Air Video and Plex (last time I did a comparison, I think I found Air Video to have the edge in PQ). This will require running a server app (which I think is similar to VLC's needs). But here is where you're problem may be...
You say that you're streaming it from your Macbook Air. Well, the Air is a great machine (I have a 13" 2011 model that I love), but I don't think I'd trust it to be up-to-snuff at doing on-the-fly transcoding using the Air Video, Plex, or VLC server apps. Keep in mind that if you're playing a non-MP4 video, your VLC app running on your Air is doing transcoding. That requires CPU power. Then, it's got to stream it wirelessly to your router, which then transmits it to the ATV. So, a couple of network hops going on, too.
In your case, you mention black bars and such. If you're using AirPlay Mirroring, that's another strike against you. I've found AirPlay Mirroring to be "neat", but I think it's better as a presentation tool (e.g., showing your desktop), and have not had luck Mirroring video from the NFL Game Rewind website. The video will play smoothly on my Air, but drops frames when Mirrored.
Just for fun, I recommend you try installing both the Air Video and Plex server apps on your Air and experimenting with those. Note, though, that anything that involves a computer doing on-the-fly transcoding and then AirPlay streaming, will result in stereo sound only.
You'll probably be better off doing one of the following:
a) Converting your videos to MP4 (e.g., using HandBrake)
b) Running VLC, Air Video, or Plex on a more powerful desktop in the house that can do a better job of on-the-fly transcoding.
c) Get yourself a sub-$300 nettop, install XBMC or Plex, and hook that up to your TV. Or, if you want something cheaper (but not as nice of a UI), get something like the $100 WDTV Live (which is special among $100 boxes as it doesn't require another computer to do on-the-fly transcoding for it).
d) Get a Thunderbolt-to-HDMI cable (I got a non-Apple one for less than $20) and play your videos directly from the MacBook Air.
