I shoot with a SONY HDV camera and want to upload footage to Vimeo or Youtube.
Just wondering if I should use Constant or Variable Bit rate and what rate should I use. Thank you.
Don't worry yourself about this question, it is the least of your upcoming problems. You need to choose appropriate color space,
codec, bitrate, and total size first. The CODEC choice is your main concern.
VBR / CBR could be an issue if you are looking at long form production to a DVD as Hollywood does when they encode a title of a 90min movie (plus bonus features) to a very high quality setting for the DVD. Then the VBR may be of some use when the encoder ( did you know they use $3,000 licensed encoders) instead of the "free" ones provided by SCS.
Either the MainConcept or Sony's AVC/AAC would work. However, thanks to MusicVid and others, many on this forum prefer the "Sony Vegas Pro > DNxHD > HandBrake> YouTube or Vimeo workflow ." http://www.jazzythedog.com/testing/dnxhd/hd-guide.aspx#lbr