Between the two: it's certainly better than DVD, as HDTV is broadcast in either 720p (progressive) or 1080i (interlaced) resolution, whereas DVD is 576 lines. But Blu-ray is even better than HDTV at 1080p (progressive) resolution, which means all the lines are scanned on the screen simultaneously, rather than interlaced (meaning odd and even numbered lines are scanned on the screen alternately).
Of course, much also depends on the quality of the film transfer: we've seen some superb Blu-ray discs, and some less-than-good ones. The same applies to HDTV: most of the BBC HD broadcast material looks good, for example, but if the quality of the original film is less than perfect, it may not look quite so good.