I’d probably stay away from Samsung. That being said, I choose Android over iOS for a number of reasons. Don’t get me wrong, Apple hardware is NICE, you’re gonna have consistent software development and a real plug and play experience. But as was said, iOS is more set-it and forget-it. (Of course there’s always jailbreaking).
As for Android, I wouldn’t worry to much about sync vs. apple. Google’s cloud covers pretty much anything you’d want to sync, they’re adding new services all the time, and it’s free. To get the same level of sync and data management on the iPhone you need to pay for MobileMe.
The thing about Android is not so much the number of OS versions, but the user interfaces and bloatware that different manufacturers skin up Android with. They all do it differently and it can turn an amazing piece of hardware into a piece of shit. If you go Android, my suggestion is to start with good hardware, and pick a manufacturer/carrier combo that has a decent reputation as far as what they do to the vanilla operating system. Don’t trip on the number of Android revisions - there was a lot of experimenting among handsets in the early days, but now Google has solidified the framework and plans are to be releasing a new version maybe once a year. You’ll see Android handsets and applications getting a lot more consistent from now forward.
HTC and Motorola have some slamming handsets right now.
The latest moto UI is much better than the motoblur stuff.
HTC Sense is a very nice UI.
Of course if you’re savvy, you can root your Android phone. I consider this a must, and should be honest and say that I wasn’t totally satisfied with my phone until I did this. But now I’ve got free Wi-Fi tethering/hotspot, a custom ROM and kernel, overclocking, undervolting, crazy-ass battery life, and best of all, can remove all the crap that Sprint put on the phone (EVO 4g).
Unfortunately as far as serious music/midi apps, Android is not there yet. So if that’s a big draw for you, iPhone is a better bet. But there are a lot of really smart devs out there coming up with new things all the time, so it’s just a waiting game. It’ll get there.