There are many discussions on this, some swear by the glass and the others swear by better bottles. Searching for better bottle should turn up some of them. There are safety considerations with hot liquids or dropping the glass carboys causing then to shatter and spray shards of glass. Some just aren't convinced that pet can be used for aging, or will cause off flavors from previous batches.
I use the PET Better Bottles and have been happy with them. Some of the cleaning compounds make the carboys very slick until rinsed off, this applies to both types. This subject is about like talking politics.