2 & 4 are compression algorithms. Either can be over compressed, saving bandwidth but resulting in poor PQ. The benefit of MPEG-4 is that ROUGHLY half the bandwidth can be used to produce the same quality picture.
In a nutshell, there are, I submit, two criteria for deciding today between D* & E*:
If you MUST have the NFL Sunday Ticket, and are willing to sacrifice all else, and pay the price of about $200 or so, then DirecTV (D*) is your choice.
If you want the best PQ and the most HD, then Echostar (E*) is your choice. E* has more national HD channels than D* due to Voom, and is putting up HD local channels just like D*, although at a slower pace. Plus, measurements have been posted about the resolution and bandwidth used by the satcos. D* compresses more and has measurably lower PQ. E* recently tried lowering their PQ, but has seen the light and will shortly return to the high PQ they provided before. On 1/5/06 E* will add even more VOOM HD channels, so there will be 15 VOOM HD channels plus the other HD.
Another consideration is the DVRs, receivers, etc. D* has dumped Tivo, although some units are still available if you ask for them. There is no Tivo MPEG-4 HD D* DVR and probably never will be, as their contract expires 2007 and they are being phased out by D* now. D* has a new provider. E* is now distributing new MPEG-4 capable boxes. I'd recommend getting the 211 or 322, and later, the 622.
The E* 942 has a great rep, but may or may not be upgradeable to MPEG-4.
