I develop for both iOS and Android - DragQueen was the first simple app released. There's a major one coming. So I have both Android phones and tabs and iPhones/iPads.
There are a lot of equivalent things about the different platforms. There is sort of no question that the iPad platform blows away the Android tab platform though. For that reason, I think things tip toward iOS. I honestly think that an iPad is the single best thing you can do to improve your cruising on a boat today - between weather, information access, navigation assistance, entertainment, email, and a thousand other reasons, the iPad is running away with uses on a boat. If you're going to have an iPad, it's much better to also have an iPhone.
For other boating related apps, I think there again, iOS wins. There are some equivalent navigation apps. Navionics is probably the best example. But even there, the Android app is a few generations behind the iOS one. There is no Transas/C-Map/Garmin/Navimatics/etc navigation versions on Android. In fact, on Android, there are very few boating navigation apps. There are about 20 on iOS (maybe more).
In general, there are much fewer apps and fewer choices for Android. I'm in a pretty good position to know why too.
If you look at my own DragQueen stats, 6,000 people have downloaded it on iOS. Today about 300 people have downloaded it on Android. I've talked to other developer friends with apps on both platforms. The ones on Android just don't make money (or get downloaded - mine are free). The ones on the Apple App Store make money. This happens across the board. So if you were a developer looking to create a killer application, which platform would you develop for first (or only)? Why don't Android users buy/download apps?
The major app I'm writing works on both platforms (and Windows and Macintosh native). For me, I want everyone to be able to use it even if Android users account for only 10% of the downloads. But until more people actually use Android apps and download/pay for loads of them, developers aren't going to be spending their time on it.