I'm doing UI/UX/Design for iOS for living and right now I'm being torn between what to do. Obviously sticking to 5s is not an option anymore, and obviously in terms of interface and layout 5s, 6 and 6+ are all different. So which one should I buy? Looks like it would be awesome to have both, but at the moment I can afford only one and need to make a hard decision. Thoughts?