i use V-downloader
to me its the simplest..
all ya gotta do is paste the link into the software and it does it for you.
it gives you different output formats to pick from like avi, mp3,mp4 etc.
p.s its free!!
I use Real Player, each time you watch a video on YT a small box in the corner will pop up giving you the option to download it. It's tonnes easier than copying, pasting and then having to wait for it to connect etc.
Which can you use to download a video with HQ version?
If I download something off You Tube, it's usually the audio I want..in that case, I use a program called MP3myMP3 and record the audio directly. Works great.