Right now i have a DishPVR, but i've owned a tivo and replay, Tivo is much better. Older 5040 series Replays can stream video to your computer (dvarchive.sf.net) Tivo can be hacked, but it's a mess and i didnt have the ambision to do it. DishPVR's can be copied too but it involves taking the disk drive out every time.
http://www.tivocommunity.com/tivo-vb/
great tivo fourms.
DishPVRs suck to cuz you have to scedule everything, tivo is nice and will give you season passes and record shows you might like (some you wont but tivo deletes them first anyways.
Commercial skip isnt a 100% and kinda anoying when it's wrong. Tivo just hit 30sec skip 4 times and your back to your show.