We provide two different PVRs, because some prefer one over the other.
For the US, there isn't much of a choice, we need it to use the majority of tuner cards, and options available to us.
For the UK, it's a 50/50 wash, MythTV is needed for MHEG interactive services. VDR works very well here too if you don't need MHEG.
For Europe, DVB is prevalent, and VDR was designed to work here.
VDR is a very lean piece of software, and it has a number of advantages,
* Fast to start
* Fast to tune
* very out of the way UI
MythTV is a bit bigger, and has more features, some of them:
* for those with good guide sources, many more scheduling options
* the ability to distribute tuner cards to media directors as well as the core
* currently integrated into the setup wizard for those who have supported tuner cards AND a SchedulesDirect account in the USA.
So it all depends on your needs.
-Thom