Although my question is similar to another about an interface for Pro Tools/Preamp for field recording with a portable recorder (H4n aswell). I'm not as experienced as others on this site so I was wondering if you guy's could give me some insight into choosing the right one to give me more long term use. I personally think the MixPre-D would be better since I don't have to worry about external power supply and after reading Varun Nair's post about the USBPre-2 it sounds like it a bit of a pain to work with the H4n, but I really don't know for sure, thanks for the help.
If you're planning to do a lot in the field with whatever you buy, then I think you're on the right track. The MixPre-D would probably be the better choice.
The USBPre-2 is not as well suited to field work. It can do the job, there's no doubt about that. It's just requires a few extra considerations.
If you're looking for something to use more as an I/O interface, and you're only considering these two units, the USBPre-2 is going to be a better choice. While the DIP switches are a bit cumbersome, it's a more flexible unit for that purpose.
I totally agree with Shaun and if you are just looking for a solid front end for your recorder to use in the field you might try and find the original mix-pre used, which has since been discontinued. Personally, I think it sounds a lot better and it has a much creamier sounding limiter.