I just got my DFX maybe a month ago, and I love it, my detector before that was a turn on and go Fisher F4. The preset programs the DFX has are very easy to use and to modify as you learn what you like and what you dont like. The presets are pretty mild so that they work right out of the box in the most locations with no problems, so once you start to learn more about the detector you can tweek it for even better performance. The DVD that comes with it has lots of good info also. I personally chose to go with the standard DFX. The 300mm coil is nice and from what I have read will go a little deeper, but I did not have the money to buy a smaller coil to complement it for those times when the big one is just to big. I will just get the DD coil down the road when I can afford it, but that is just my situation. Good Luck with your decision.
edit: you might also want to check out dfxonly, just google it.