These are experiences/opinions. They are confined to the more popular HD-capable RPTVs.
It depends on a few things. Whatever RPTV you buy, it needs an ISF calibration, preferably with a Sencore machine to get the best picture. This is not always timely or easy to find.
The Mits Platnium line is a good value, but like all Mits... it needs some tweaking and attenuaters to solve the red push problem. It doesn't have the best picture with NTSC feeds, although DVD and HD is very good. It is also upgradable with the purchase of a firewire input for another $1K. But since this is an interim TV for you, I wouldn't really worry about that.
The Toshibas have great out of the box pictures and DVD and HD is about the same as the Mits Platnium. Some say better, some say not as good. I think they're too close to call. Even after all the tweaking, the NTSC picture on the Toshiba is better due to the better line doubler.
The Pioneer Elite and Mits Diamond line are the best in this class (haven't seen Runco, Loewes, Fajorda). But they are pricy.
I think the Pioneer Non-Elite is the best TV for the money. It shares many of the parts of last year's Elite and is every bit as good as the Mits or Toshiba with all sources, if not better. I think the build quality is a little better also, and has a more attractive cabinet. It's flat black, not the piano gloss of the elite.
I have the Toshiba 57HX81 and although it's pretty good, if I had to do it over again I would buy the Pioneer non-Elite.
Also, Mits makes a 46" or 48" model that is a table top RPTV. This is nice because you can put the STB, DVD player, and HT receiver under it and not take up as much space as you would with an audio rack beside it. This would make speaker placement easier in my case.
I didn't really like Sony's RPTV last year when I was doing all my research and thought it was overpriced. I understand the new ones are better.
Never seriously looked at the Hitachi, Panasonic.
The burn-in issue is a result of the contrast being too high. Even so, I admit the stationary, bold icons on some channels makes me nervous sometimes.
As far as 16:9 or 4:3, It's 16:9 all the way for me. But don't think you will never get black bars on DVD with one. Some movies are shot 2.35:1 instead of the widescreen's 1.85:1 ratio and you still get them. Stretch modes can do away with them but can distrort the picture. Even so, it's better than watching a 2.35:1 movie on a 4:3 TV. The bars are huge then!
I think the Toshiba 42H81 for $1500 is a good deal. I've also seen the 50H81 for about $2K.