Think of how inconvient changing miniDVD's is going to be, every 30 minutes. If I had to choose between the two I would get the SD camera because in the future there will be higher capacity SD cards, so long as the camera supports them. Can you post a link to both cameras?
Personally if I had to get a camera on the cheap I would get the Canon ZR950, it uses mini DV cassettes that can record 80 minutes of digital video. Its 240 bucks and has free shipping and no sales tax if you out of state,
amazon.com and
newegg.com both have the camera for the same price, might be worth checking out. It also has a SDHC memory slot that can capture video and still photos.