Hi Fumado, you can consider the following differences between the Slingbox PRO and PRO HD.
The Slingbox PRO HD currently offers support for the Slingplayer for Ipad and also for all the current versions of the Slingplayer mobile.
The Slingbox PRO HD has an Internal tuner for Analog and Digital signals while the Slingbox PRO only has an Analog tuner.
Please check the Link below for a list of the features of the Slingbox PRO HD.
The analogue tuner part isn't entirely true. My UK spec Pro has a digital Freeview tuner built in. I think it can do analogue as well, but I mainly use the digital.
@OP - The digital tuner on the Pro HD offers 640x480, while the UK Pro only supports a terrible 320x240. I'm a bit disappointed with it really (320x240). But I didn't know how good the technology was going to be so I refused to pay the premium on the Pro HD. Some of the inputs are different between the models, I think. Mine came with the HD connect dongle but I haven't tried it out yet.
The Pro HD supports higher resolutions too. But, you're going to need massive upload bandwidth to run them (+2Mbs). The Pro is also retired hardware, or whatever you call it! New features could be added to the Pro HD but not the Pro.
If you are going to use digital tuner, go for the Pro HD.
If you're going to be controlling a Sky box or other STB, then save your money and buy the Pro. It's resolution/picture quality is fine at 640x480, streaming at around 2.2Mbs.