Which one do I buy Pre Ject Debut III or Rega P1??

rega because of overall quality

I third the Rega (and the Music Hall would be my second choice, ahead of the Project). In addition to the better arm, as Mofimadness says, the Rega will have better soundstaging and imaging, if these are important to you, as well as better resolution of instrumental and vocal timbres. It is also a little more 'set-it-and-forget-it' than the other two, if you are not very technically inclined.

Thanks, I appreciate the feedback. Now, if I did decide on purchasing a used turntable, for less than $400 which one would be the most musical, warm sounding, and produce a great soundstage for 70's and 80' disco music?

For 70s and 80s disco? Technics SL-1200.

Wendell

My first choice is Rega P1 because it has a better arm in my opinion than the Project or Music Hall. I also think the Rega has a little better acoustical dampening.

The Technics SL1200 is still a very good table. The arm was a perfect match for many MM cartridges back in the 70's, 80's to present. A Shure V15 Type 5 was a wonderful match for home listening. You most likely won't have any hum issues with the SL1200 but it will cost more than your Project or Rega. I also think the TEchics has better acoustical dampening than many tables in the price range you are seeking because it's built for rugged environments. Plus you get some great speed & pitch controls that you won't get on any of the tables mentioned other than this one. It is direct drive and some people have problems with that. You could do alot worse in turntables.