Well, i've had both and preferred the Q9c mainly for the exposed keyboard, smaller profile, built-in gps (that worked with any gps app i installed), stereo speakers, plus Documents To Go for Win mobile is just amazing. One more thing, the phone's call quality is very good (it blew my Treo away in this regard), and bluetooth actually works so very well (it's a Motorola afterall).
Specs-wise, the Mogul is more powerful but all that power is seriously hobbled and crippled by the lousy memory problems it has. The Q9c runs Win Mobile 6 standard (Smartphone), so no touch screen but i did not miss that at all. I was able to find Smartphone versions of all my favourite apps anyway. It has a slower processor than the Mogul so it doesn't breeze through everything at the same speed but it's good. I installed the Smartphone version of Opera Mobile (NOT Opera Mini) and it rendered what i consider complicated websites very well and fast too.
It's not for everyone, especially the folks who like bigger screen phones and built-in wifi (you can get a mini-sd wifi card btw). Coming from a Treo 700Wx, it suited me fine.
I ditched my Mogul long ago and went back to my Treo, but of late i have been using the Q9c (i go back and forth with Treo 700Wx and Q9c
)
Hope this helps a bit.
Oh one more thing i forgot, Windows Media Player on the Q9c can natively handle rtsp stuff from m.youtube.com. I was surprised at that actually.