Mini DV is certainly best for picture quality and the ability to transfer footage from camcorder to computer is much easier than other formats. As far as it being the 'most common' type, it's hard to say as you would have to see sales figures of the various formats over the past few years. If you want to have the best picture quality (haven't used HD video yet, so can't comment), then go for Mini DV over hard disk camcorders and DVD camcorders. Hard disk and DVD camcorders are very convenient if you don't plan to do any editing after shooting. The file formats they use compress the picture quality much more than Mini DV and their file formats can cause a lot of problems when it comes to editing. A standard Mini DV tape records for 60 minutes in SP mode, which is the recommended mode, do don't use the LP mode on your camcorder if it has one. Also hard disk camcorders use USB to transfer footage between the camcorder and computer and the DVD camcorders use a version of MPEG, which compresses video a lot - it needs to as you can only record up to 20 minutes of video onto a mini DVD disc. Whereas Mini DV uses Firewire.
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