All three Superadios are about as good as it gets for MW DX and listening -- although the Superadio 3 was problematic early on, and later on. Their mid-run was pretty good.
The SR2 is usually considered the best of the three, although I haven't noticed mine being any better than the others. My SR2 took a dive from a refrigerator and still works. They're built like tanks. And yeah, if you decide to take the back off, be very careful of the power switch. It breaks easily.
One of the best features of the Superadio 2 (and other Superadios) is the sound. A lot of MW DX radios today have a muffled sound compared to Superadios -- so with the SR series you not only get good performance but good sound, too.