I didn't believe what I saw in your question until I fed the titles into Google.
It seems you want to compare similar Hauppage TV cards where WinTV-HVR is a PCI connection.
HVR900 is a tiny device which is external to the PC and connects with a plug into a USB(2)port.
The first which is conventional costs about 2/3 of the USB version.
Having used neither I can't recommend one over the other.
Based on older devices, unless portability is a big factor, if you only need it for a static PC, then stay with the tried tested (and cheaper) PCI card.