FYI, there is a third option...
Better Bottle is a plastic carboy that has all the benifits of both. (never used one, but with Glass Carboys getting more expensive, that is probably the route I will go for the next one.)
It is light, low Oxygen permiabilty (pretty close to glass, but better seals than plastic buckets), not dangerouse if broken...
However, plastic scratches easier than glass, so you need to be more carful when cleaning plastic, never use a green scrubby..etc.
I have used both Glass Carboy and Plastic Buckets for abut 5 years now. Some batches I use the glass (it is fun to watch the fermentation process), some I use plastic buckets. I like the convienence of plastic buckets vs carboys, but if I am going to leave a beer in the container for more than three or four weeks, I ususally choose the carboy over the plastic bucket.
Also if you get a Carboy, get a Carboy parka or brew hauler device to allow you to pick up the carboy by straps instead of the neck of the bottle.
I guess my recomendation is start with a plastic bucket, and then as time goes on, you can add a carboy if you desire. I like the ability to clean out the bucket easier, and quite frankly, cleaning and sanitation is really the biggest part of brewing.
Also, what I found is that after a while, having one beer going at a time was not enough, and I actually have two buckets and two glass carboys right now. Near Christmas time when I am brewing for parties, I have all four in play!
Good luck and have fun!