Considering that the DMP3 is sold as a 2 in /out preamp and cost about as much as a yamaha mg10/4, I'd have to say the DMP3 is better overall at what it was designed to do. I own a DMP3 and it gives a lot of gain and doesn't add any color that I can detect. Moreover, I'm having an mg12/4 on backorder right now, so I'll let you know what the difference is.
Edit: Whoops, I read your question as "Which one is better". I'm not sure if the DMP3 is a step up that's worthwhile if you already have an mg mixer, as it is better, but not one of those higher end preamps.