I also went through 4 dInc's and finally told them to send me a DX. Here are the pro's and con's from what I can tell between the two after a month of use:
Pros with the DX
- screen size (huge and I love it)
- battery life (huge difference, I went two days last weekend and have never gotten through a single day with the dInc)
- build quality (can't stress this enough, it feels solid, no more creaking battery covers, dust under screens, etc)
- reception (I can take calls in my brothers basement now where the dInc and original Droid can't, very impressive. Basically, if there is signal, I can make/take a call)
- voice quality (no more washed out sounds and can hear people clearly again)
- Docking station (with the big screen, it is very usable in the car as a navigation system)
Cons with the DX
- screen viewing angle (not a huge deal, but unless you're pretty well straight on, the screen gets very washed out when tilted)
- hands free calling (this is a big one for me. I use bluetooth hands free calling constantly and neither the Voice Commandor or Vlingo hold a candle to the one built into the dInc)
- software (It cost me probably $10 in apps just to recreate the look and feel of Sense. Blur sucks and I liked Sense much better than the stock android look/feel. Still probably not as responsive as Sense, but close enough)
- physical buttons (I know most people would put this as a pro, but pressing the buttons with your thumb on a big screen would be easier if it wasn't a hard button. I also don't ever remember hitting those buttons by accident in 6+ months with the dInc, so I don't understand how so many people think that's an issue)
Overall, I definitely like the Droid X over the dInc, mainly because of the screen size and battery life. If Motorola would build the phones and HTC provide the software, it would be a superphone. The voice commander/vlingo thing is still frustrating as it was PERFECT on the dInc and both of these apps suck (voice commander literally takes 30 seconds to start and vlingo either calls the wrong person or doesn't work when I hit the button).