I'm an Android and iOS user, and I haven't had any problems using either platforms with the Pebble (one reason I got it was for compatibility).
There may have been issues early on but there has been lots of software updates to it. 2.0 was a major one and 2.6 came out last week with full iOS 8 support. Seems to work just fine on my iPhone 5 running iOS 8, and my HTC One M8.
There are some differences in the Apps you can install, since Android is more open on allowing system access (see phone battery, send SMS through watch), but most apps work on both iOS and Android and notifications on the iPhone essentially mirror the notification center, where as on Android it's on a per app basis and you have to sign in to each email account and app through the Pebble. So I actually prefer the iPhone in that instance.