For ease of cleaning, glass wins since it isn't easily scratched, and will withstand harsher cleaning methods over time. Also, plastic will have to be replaced periodically as it can get stained and / or leach over time.
Plastic isn't nearly as fragile or heavy as glass, so it wins on those fronts. It's much less expensive than glass, which is why so many brewers start with plastic. It's also much more versatile, and can be used both for fermentation, as a cleaning bucket, a bottling bucket and for storing all your kit in between brewing.
Both work fine for basic fermentation without effect on the finished quality of the beer. What's more important is sanitation of the fermenter, not whether it's plastic or glass (unless you are aging, which you should never do in plastic).
We've only just begun selling Better Bottles at our shop, so don't have any customer feedback on how well they hold up over time.