User-editable dictionary for the keyboard is nice. For example, I type “stevenf” a lot, so I added it to the keyboard dictionary. I also mistype it as “stevebf” a lot, and unfortunately my iPhone learned this misspelling and I have to correct it every time. There’s no way for me to delete this misspelling from the iPhone’s dictionary, short of brain-wiping the iPhone.
Steven Frank’s notes comparing the two, with some good points.
Highly dependent on Google account. For example, Calendar can’t even be used without being logged into a Google account. In a way, you are a just trading a certain amount of Apple lock-in for a certain amount of Google lock-in.
I use a standard IMAP server for email. Gmail and Mail are two separate apps (why?) and the standard mail client is very much a second-class citizen. (Cannot move a message to another folder, for example. It’s just not possible.) A third-party fork of the standard email client (called K-9) offers better IMAP support, along with its own set of weird behaviors, fractured GUI, and regrettable Dr. Who icon.