Absolutely DVR! Or not.
If you are a DirecTV customer and you can live without HD then one of the portable automatic antennas and a DVR is a complete no-brainer. Watch and record whatever you want without restriction.
If you are a Dish customer you CAN get HD but you will not be able to use many of the Dish compatible antennas and you will not be able to record programming on 2 different channels if they are being broadcast on 2 different satellites.
DVR's are THE BOMB! If you think what you want to do will work with the service you have selected then you absolutely should get a DVR.