Hi,

in short:
EZdrummer 2 is more oriented towards writing good sounding drum tracks as quickly as possible. Pre-produced Presets in the EZX expansions with limited tweakability.
It has functions like Tap2Find (find grooves), Edit Play Style (manipulate grooves on the Song Track) and Song Creator (suggests Song Track parts and structure).

Superior 2 is aimed more towards the producer who wants to be able to control every kit piece, articulation and microphone. It is also easier to customise if you’re an E-drummer.
It has a mixer where you can add and edit EQs, Filters, Transient Designers and Compressors. You can also add Bus+Sends in the mixer.
The Superior SDX expansions are much bigger and have more instruments/tools to choose from. Superior 2 can also load EZdrummer 2 EZX:s.
Superior 2 also gives you control over MIDI note assignments, Envelopes, the possibility to add drums from other expansions as X-drums, which can be stacked with another drum or added to the kit.
It does not have the Song writing functions that EZdrummer 2 has, only a groove browser.

Hopefully this clarifies.

BR,
John