Depends what your used to and what features you want....Dm500 is similar spec to the TM500/Tm500 Super.
TM600 has PVR and USB and is more like a DM600. If your looking at client only TM might be worth a look.
If your looking at wanting a server using CCCAM this doesnt work properly standalone on TM500 or 600..
Also your restricted to only the UR image on TM, you dont have any choice of images. Also poor track record of software support and bug fixes on TM linux recievers so far.