If you buy a plasma, DLP, or LCD - let's say the resolution of what you buy is 1280x720 pixels. Then that is what it will show.
It doesn't matter if you send it 480i, 480p, 720p, or 1080i - It will scale and process everything to 1280x720 (or a 4x3 version thereof). All fixed pixel devices have a scaler of some sort inside them and the quality of them definitely varies from model to model.
One thing I have to point out is that the ORIGINAL source really, really matters a lot. That is, if you have a mini-DV camera and you shoot some video and feed it into a really good TV you will see how incredible the quality of 'standard' definition TV can really be. Digital cable (sometimes) looks better than DirecTV and both look better than analog TV. But even DVD doesn't match the quality of regular mini-DV.
This really is the bigger issue, instead of scaling questions. Though scalers do matter, most manufacturers seem to have contracted to put good quality scalers into their products and the day of spending thousands for a Faroudja outboard scaler are pretty much up (a few will disagree, I know). Faroudja, being run by some bright people, has quite a reputation and has various chips that they sell to plasma and projector manufacturers to allow that technology to go into their product.
A review would be hard as you would need a good 10-20 displays and feed them all an identical source to do a head-to-head shoot out. In my experience though, the better a display is, the worse SDTV looks on it. It happily shows in exacting detail all the flaws present in a 480i analog image.