Which is the best format to download DVD movies, e.g AVI,MOV,WMV I find it all abit confusing!

The very best format would be .mpeg since it's the format used for DVDs (there are several .mpegs, but I thing MPEG2 is the DVD one).
The .mpeg one is also one of the "largest" (if not the "largest") format, in that it's the one that will take the most HD place for a given movie (for an hour-long moviein decent-quality encoding, you should file sizes of 1Gig and above)
.avi is a very good, common format. It has decent quality and is less cumbersome than .mpeg, with the respective loss in quality (the same hour-long movie would be around or over 700Meg at decent quality).
.wmv is bad.
->For a more objective opinion, .wmv is a rather low quality format, but, as would be expected, it is also a lot less demanding HD space-wise. The problem is that because of the way it is encoded and because most people will play it in Windows Media Player (which allows the following), .wmv you find on P2P networks are too often fake files for my taste: they will very often just be links to some fancy site (=best case scenario)
.mov is, AFAIK, more of an Apple format (as .wmv is a Microsoft format). It is a decent format but takes more space than .avi.

Well, I've said a bit more than what you prolly wanted to hear, but I felt like writting.

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