I have both. I have cooked with the DX2 many times and it is awesome. One of the best investments I have made for long cooks.
I recently purchased the Party for use when I don't have electricity or need to run another smoker (without the added cost of another DX2). That and I was curious to see how it worked. I have only used it a couple of times but it worked like a champ.
I don't think you can go wrong with either one but I like to plug in the DX2 and not have to worry about batteries.
LBGE, 22.5 WSM, 14.5 WSM, Weber 26.75 OTG, Weber Performer, Backwoods chubby, Speed of light fast Packer green Thermapen, Speed of sound fast red backlit Thermapen, Ultra-fast American flag Thermapen