Eggs and ATACs are equally mud worthy. I have a pair of candys and they shed mud as well if not better than ATACs.
To adress your question, if mud is your concern, then even candys are probably "overkill." The perception is that the extra $$$ of ATACs is due to their bombproff construction. The ATACs also don't release if you hit a rock or stump, as the eggies do...not a big deal in my experience though.
If you don't ride in much mud, consider a pair of Shiman os. the 525's (I believe) won't break the bank, and are a pretty bombproof pedal in my experience. (747's, in my case.) My Candys, on the other hand, recently required a rebuild when the tiny cartridge bearing disintegrated in one of my pedals. This led to a general loosening of the pedal and the pedal body eventually worked its way off of the spindle mid-ride. I don't believe that this is common, but it's the first time I've had a pedal do something like that.
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