We tested syncing a 50MB file with both programs, with interesting results. By default, Dropbox is significantly slower, because it automatically throttles your upload speeds. However, this is all tweakable in Dropbox's preferences. You can change how fast it uploads and downloads files, which is great if you don't want it to steal bandwidth from other important things (like video chatting, games, or BitTorrent). Google Drive doesn't give you these options, which is kind of annoying. With Dropbox set to "Don't Limit", it uploaded files at the same speed as Google Drive in our tests.
However, Dropbox also has LAN sync, which means transferring files to another computer on your network is going to be a lot faster than Google Drive, which will download it from the servers instead of the other computer. After uploading our 50MB file to Dropbox, it took less than a minute to show up on our other machine, while Google Drive took about 3 more minutes.
s section by a mile.