Can I suggest that anyone wanting DAB radio goes to :
http://www.ukdigitalradio.com/coverage/search/default.aspthen put your postcode in.
While DAB coverage is great in most urban areas it can be non-existant in some rural areas. It is very much like the comparison between analogue TV and digital TV - in fact its identical. You will get better sound quality as FM stereo only has an audio bandwidth of 15kHz whereas 128kbps MP3 (common DAB radio quality) will have an audio bandwidth of about 18kHz. In short it'll sound almost as good as a CD. For me (I'm nearly 40) I couldn't tell the difference between 128kbps DAB and a CD - I've tried and I can't tell the difference except on some
very quiet classical pieces. You can tell the difference there as background noise (nearly silence in the studio) sounds artificial on an MP3. In my humble opinion of course - I am no audiophile
The way it is identical to digital TV is that it has roughly the same coverage as TV (DAB is broadcast at about 240MHz) and that if you get a signal which is bad enough then you will simply get a load of whistles and pops rather than intelligible audio. That's the way "digital" audio/TV in the UK works, so no hearing static on DAB - you get perfect audio or nothing. Well you can have a channel that comes and goes as with AM/FM but it won't be something you would listen to.
In my opinion you WILL get what you pay for with a DAB receiver. We have two - a no-name portable and the Pure DBX-25 I mentioned in another thread. The portable gets 17 stations and takes perhaps 2 to 5 seconds to tune to another station. The DBX-25 gets 31 stations and on 20 of those (or so) it takes under a second to tune to another station. You also need to look at the maximum bitrate the DAB radio can manage - for new (decent) radios it should be 192kbps. I suspect that the portable we have only "receives" 17 stations as some of the stations are at bitrates it can't handle.
Oh there are also things called "subchannels" - like for example Radio4 LW gets transmitted as a subchannel on the Radio4 DAB multiplex. Basically its possible to add another channel temporarily for an event (eg cricket on R4 LW). This normally results in (for example) R4 DAB and R4 LW sharing the bitrate R4 DAB normally gets - practical effect might be that R4 DAB would go mono during the R4 LW cricket broadcast.
If you are asking "Will this be better than AM/FM?" then the answer is oh yes, there is no comparison
Check your coverage first though.
Hope this helps.
Edit - R4 LW = Radio 4 longwave.