It sorta sounds to me like you have only one disk. No matter which brand or capacity you go with, you must have two of them. Of all the things you need to have back-ups of, memory is first on the list.
The different strategies on how big and how many is endless. For me, I've found 8 gig works great and that's using NEF for about 95% of my work. I shoot a D3 and it has slots for 2 disk and options on how they're used. Mostly, I use the second 8 gig card as an overflow and it seldom gets used. I also have another pair of cards attached to the neck strap and my back-up D700 has the same set-up except it only holds 1 card in the camera.
I've never had a disk break but it's going to happen sometime and I'll get all paranoid about disk usage, life expectancy and brands and all the other stuff you're wrestling with now. The only issue I've ever had with cards I caused by using the computer to erase the cards instead of reformatting the card with the camera. Whatever you end up with don't skimp on quality. Buy critical camera gear at reputable dealers and have confidence in your tools.