They are all different so comes down to your needs really. I've owned all of them except the NAD but I have an NAD integrated I use for a bedroom system. The Emo with what I had was bright but I do recall that both it and the Para 2100 have HT pass through as well the ability to easily add a sub a 2 channel system.
The 2100 does have a phono section and the Emo does as well but neither are mind blowing but the 2100 IMO was a better phono section. The P3 also has a phono section which is better than the 2100.
Personally I think it will also come down to the other parts of your system. IMO the P3 would have the best SQ, with the NAD probably sounding nice as well, normally warmer in SQ, the emo I feel is a bit bright and the parasound 2100 is a nice all around unit that is not too hard on the wallet.
So the list for me
1. P3
2. 2100
3. NAD
4. Emo
The 2100 does have a phono section and the Emo does as well but neither are mind blowing but the 2100 IMO was a better phono section. The P3 also has a phono section which is better than the 2100.
Personally I think it will also come down to the other parts of your system. IMO the P3 would have the best SQ, with the NAD probably sounding nice as well, normally warmer in SQ, the emo I feel is a bit bright and the parasound 2100 is a nice all around unit that is not too hard on the wallet.
So the list for me
1. P3
2. 2100
3. NAD
4. Emo