It is all question of what you want from your box. If you just want to watch tv than you need to look at the Eurovox range or if you want a box with a lot more potential and you don't mind the fustration at the begining in installing your box than you want the dreambox. People who have dreamboxes never actually watch tv as they are too busy tinkering with their boxes.
The dm500 is cheap and cheerful and does the job but the dm600 is much better and can also take hdd for pvr. I have bot and much prefer the dm600 but it is twice as expensive as the dm500.