That depends but in almost all cases it will be both.
Keep in mind with Android you reach a large population, with iOS large revenues.
If you have a B2B product you have to go for both. If you first want to try an MVP you might want to save cost and evaluate it with one of them - whichever better fits the targetgroup.
To save cost you can use cross platform development frameworks like Xamarin or sencha or phonegap.
However there are basically two approaches you need to understand on those platforms.
1. pure native apps you get from xamarin for example
2. html5 apps with a browser client that you get with sencha for example.
#1 is better for performance and using native apis but as well normally more difficult than the html5 approach