I recommend doing your primary fermentation in a bucket and using a 5G glass carboy for any secondary.
But, don't be in a huge rush to move to carboys. I know many award-winning homebrewers that use both but tend to prefer their buckets (including me - though no awards). Buckets are cheap, light, easy to clean, easier to store, and safe. If I secondary, I use a glass carboy- or may even bottle and "secondary" in the bottle by letting it sit longer if it just needs to age. -My personal preference is to get the beer packaged and under CO2 as fast as possible and handle it openly as little as possible.. not using secondary saves a racking.
Cleaning a carboy after primary fermentation is more work than a bucket... most of my secondaries leave the carboy pretty clean so a quick rinse and mild bleach swirl is all that's needed. When I primary I fill the carboy with bleach water, let it soak a day and still need to scrub to get all the krausen residue completely clean. I don't have a drill powered "carboy cleaner" yet but building one is on my list.
With a normal 6-7G bucket, you can fill a 5 gallon carboy very full leaving very little room for O2. Same logic applies all glass, if you primary in a carboy get a 6-6.5G, if you are using it to secondary a 5G batch, get a 5G carboy so you don't leave much headspace in secondary.