Picked up a gold 5s on Verizon and will let T-Mobile pay off my etf in a few weeks. I haven't had an ios device since I sold my iPad 3rd generation (the first Retina iPad). I've been using Android phones the past few years, and more recently the past 6 months a Nokia Windows phone.
First impression is impeccable build quality. The phone is gorgeous, but I can see where people that own the 5c say the 5c feels better in the hand while the 5s is prettier to look at. The phone feels very solid and the buttons are easily distinguished by feel. I think Nokia is the only other company that can come close to the build quality of Apple. The screen does seem small because I've been using phones with bigger screens the past few years, and for web browsing and navigation I still do prefer having a larger screen. The camera is great, especially the two tone flash for low light pictures.
I like the Notification center and Control center, both of which are new versus when I used the iPad 3. I do wish Apple added something similar to widgets on Android or live tiles on Windows phone, but at least Notification center can show some of the information I want at a glance. The Google search app also has the Google Now cards that have information at a glance that I want too so that's a positive.. It would be nice if in future updates that those cards can be integrated into Notification center, but I doubt Apple would let let happen. ios is smooth and fast as expected, but I do think the competition has caught up enough now that it's not really an advantage any more (I think all the high end phones are fast enough, and the Nexus 5 and Nokia Windows phone are just as smooth to me). I don't really use any obscure apps or play games on my phone, so all 3 phone operating systems work for me.
I do hate how I can't use the same micro sub chargers as my other devices because I try to use things that are platform agnostic. But I have to say that the Lightning connector is a great plug - it's nice that you can plug it in either direction and it'll fit and it works.
I'm the type of guy that likes to switch devices every few months so it's nice that the iphone retains its value more so than any other phone. I'll more than likely switch devices again when the next Android flagship devices come out, but I wouldn't be surprised if I can do an even exchange because of the iPhone's resale value. If the next iphone does get a bigger screen I'd be very interested in it. Right now I think the Moto X is the perfect size phone - it has a good size screen but it's not a huge phone. For now I'm perfectly happy using the 5s for the next few months.