Overall Blu-ray has far superior quality. I don't usually rush out to buy films or TV series the day they are released unless it is something you are really into. There is plenty of quality Blu-rays that don't come at a premium price.
If you have a 42 HD TV than I can only really see a couple of reasons that you wouldn't buy a Blu-Ray version of a film if you have something to play it.
1.) It doesn't exist yet and there are no forseable plans to release it.
2.) It is a indie production that lacks the funds to put out a quality Blu-Ray
3.) The Blu-Ray has royally fucked with the original film(cough*Star Wars*)
Some Blu-Ray transfers are cruddy but there are often multiple releases of a film of varying quality so just do your research. As a general rule if you see Criterion on the lable than that is the mark of a quality blu-ray. Services like Netflix or Hulu Plus are also great for checking out quality shows you still might not want to spend the money on for a Blu-Ray.
Buy the Blu-ray if at all possible for stuff you know and love, I would reserve DVDs for impulse purchases
If you have a 42 HD TV than I can only really see a couple of reasons that you wouldn't buy a Blu-Ray version of a film if you have something to play it.
1.) It doesn't exist yet and there are no forseable plans to release it.
2.) It is a indie production that lacks the funds to put out a quality Blu-Ray
3.) The Blu-Ray has royally fucked with the original film(cough*Star Wars*)
Some Blu-Ray transfers are cruddy but there are often multiple releases of a film of varying quality so just do your research. As a general rule if you see Criterion on the lable than that is the mark of a quality blu-ray. Services like Netflix or Hulu Plus are also great for checking out quality shows you still might not want to spend the money on for a Blu-Ray.
Buy the Blu-ray if at all possible for stuff you know and love, I would reserve DVDs for impulse purchases