If I must have an android smartphone to make apps for it, what is my best option?

Go with the pure Google experience (vanilla Android). You can get the Galaxy Nexus from Verizon or Sprint – or go straight to Google and buy directly so you don’t need a contract.

Phone manufacturers will build UI modifications to differentiate themselves (Motoblur, HTC Sense, etc), but you end up with a phone that is awkward and doesn’t get the latest updates in a timely manner. This is important if you’re going to be developing.

Based on this table of the top ten smartphone sales, I’d go with the Samsung Galaxy S II as the best selling Android phone across service providers.

You would want a phone that runs on Android 4 (ICS) if you want to make apps that could be played on the most recent phones.
Galaxy Nexus. I think, is used by developers.

It depends on ehow forward-thinking you are.

If you want to develop for the future, go with an ICS phone like one of the Samsung Galaxy phones, though expect to pay more.

If you want to develop for the Android version that is currently the most widely used, there are a kajillion phones out that run Gingerbread, and some of them (like the Droid 2, Droid X) can be had for almost nothing as they are a generation or more out of date.

Just in case you’re under the impression you have to have the physical device to start development, it’s worth noting that the SDK includes an emulator that would serve that purpose. You can build applications without ever actually touching any of the devices they’re intended for.

It’s never a bad idea to have real world devices to test with, but if you’re buying something just for that purpose it may be better to buy several cheaper devices and start building a library to work from.

@funkdaddy thanks didn’t know.