It depends on your needs, and your use for the mixer. I think the QMX-2, has a better feature list for the price, but if you want a smaller battle mixer, than go with the qd3.
I own both, and Stevie is right, it depends on what you are doing. Currently, I'm using the Q-MX2BPM with two PS2s, a mic, and a sampler hooked up to it. If you need more than two things connected (two decks, plus a sampler/synth or a third deck), and want to freely mix between all three, the the Q-MX2BPM is your choice. The Q-MX2BPM also has an adjustable crossfader curve via a knob, whereas the QD3 only has three switch settings. I like the MX2 better in this area. The Q-MX2BPM also has built-in BPM counters, which may or may not make a difference to you. I think the Q-MX2BPM is a great buy, and gives you room to grow.
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