I have and use both better bottles and glass carboys. Having used both, I prefer the glass carboy.
The choice is a personal one - Better Bottles are fine for making mead in. They do not contribute flavors, they are easy enough to clean, and they are certainly lighter. The reason I prefer glass, however, is that the better bottles are very slightly flexible, and it seems that any sediment gets stirred up more during transfer if it is in a better bottle. It seems that I don't spend as much time waiting for sediment to settle in a glass carboy as I do with a better bottle.
On top of that, assuming that you do not break it, the glass carboy is going to last longer. Every time you clean a better bottle, you run the risk of scratching it, and even fine abrasions that do nothing more than cloud the inside surface of the bottle are going to hide bacteria in the long run. A glass carboy is never going to be unsanitizable as long as it is in one piece.