I would expect many westerners to play Kame-pact first, commonly because they'll have Romanized foldernames - and K comes before M in the alphabet.
If you keep in mind that each CD had a different producer when all of the content could have just as easily fit onto
one CD, maybe the play-order isn't supposed to matter. Shiina Ringo was pregnant, she wasn't writing her own songs, and two different guys were producing for her - so I wouldn't exactly call the collection a "unified vision".
I've always had the ritual of playing Mori-pact first. That's really all it is. A ritual is any habit you uphold, without a completely rational/researched/provable reasoning. I could be right for the wrong reasons, no reason at all, or I could just be wrong. I'm not going to pontificate Mori-pact as 'first', and act like that is totally canon.
Considering that
Kronekodow.com lists out Mori-pact before Kame-pact (despite the serial numbers), yeah, I
think Mori-pact comes first - if
anything comes 'first'.
If anyone has concrete research/sources, I would actually like to know what the "proper" play-order is, if there even
is one. But until then, Mori-pact being first - is my best
guess.