Google's default client/app for the Mac definitely isn't bad. You get a folder just like you do with Dropbox which blends well with the Finder app. However if you're not a fan of the integration with Finder and would rather it were a separate app, Archy is the way to go.
Archy is a neat little Google Drive client built specifically for the Mac. It's in BETA stage at the moment but is available for anyone to download.
You can easily do things like drag and drop files straight into the app. You can also drop it over someone specific so the file is shared only with that person.
You can preview files without having to open them up in their required apps. So instead of having to open a word document in Microsoft Word, you can preview it right there and then in the app.
Notifications are included so you know when a new file has been added in real time.
I myself am a Dropbox user but this app will be massively useful to anyone who uses Google Drive.