Well, we've got both in my family (I've got the 30BG video, my son has the 4GB nano).
I just upgraded from the 6BG Mini.
Both the Video and Nano are sweet.
If you want super small and light and don't care about video (and want/need to pay 50 bucks less), get the nano.
For me, I am really hooked on the video. It's not much bigger/heavier than my mini which I used mostly while jogging. Had trouble reading the mini to see what song was playing without my glasses while jogging, so the larger display of the videio will help.
Fooling around with the video is great fun. There are free video podcasts available at itunes along with music videos and tv shows for 2 bucks a piece. However, with the free
videora ipod converter you can convert your DVD movies and other videos for use on your ipod (and PSP).
I'm having a lot of fun with my ipod video.