I think the main question you should ask yourself is if you prefer buttons over touch screen. If so, the MX-700 is probably your best bet. If you don't really care, then there are lots of other factors.
Price is one obvious difference. The unit itself may not differ much, but with the T2 you could end up spending a lot more if you are drawn to the extras. The T2 extras however are a plus.
Ergonomics...close call. The T2 is really big and heavy, but balances well in your hand. The MX-700 is light but handles great.
Buttons...I prefer the feel of the harder buttons on the MX-700 over the rubbery feel of the T2 buttons. The touchscreen on my T2 was good. The thumb-pad on the MX-700 leaves something to be desired (center button is a bit wobbly), but at least it HAS a thumbpad. As a matter of fact...having separate buttons for transport and navigation was THE deciding factor for me to move from the T2 to an MX (500 initially, 700 later).
The screen...the touchscreen on my T2 was good, some people seem to have trouble with it. It worked well, but I could not put more than 6 buttons on it. If I went for smaller buttons (up to 12), they just got too small for me to press them accurately. The 10 buttons on the MX-700 are smaller...but you can FEEL them, which makes all the difference.
Functionality....VERY close call. The T2 has a slight edge, but it is an edge that most people won't need. It is a little more powerful in macro programming, and the use of the screen is more flexible. E.g. with the T2 it would be easier to create a wizard-like activity based menu.
Editing software...again a close call, but I'd give the nod to the T2 Designer software. Don't get me wrong, the MX-Editor is very good and definitely adequate. But the T2 Designer is just that little bit better. One example, with the T2 you are using a separate library with IR commands that you can drag and drop to the buttons. That way you can first create your own library and save it independently of your button layout. With the MX, your library of commands is integrated with your button layout.
For the rest...I prefer the normal batteries in the MX over the rechargable proprietary battery in the T2. I really like the MX-200 sidekick remote, eventhough I thought at first it would be useless (it is an excellent babysitter remote).
All in all my preference goes to the MX-700. But then I am totally a hard-button user...
