Call quality! I picked up a Verizon s3 a week before the iPhone5 came out. It was constantly dropping calls. Both stock and rooted with CM10 installed. I took it back the day I got the iPhone 5. No regrets.
I used the GS3 for a month waiting for the iPhone 5. I really liked it for roughly 2 weeks...I also thought I might be interested in keeping it until little things started to annoy me.
As I read through all the posts, I was able to fully realize the main reasons I returned it for the iPhone 5. There is three, and I cannot seem to pick just 1 as the main one.
1. Call Quality - Like the post above, I had issues with this. Also, I hated the speaker in the earpiece. It sounded awful when I would talk on the phone.
2. AirPlay - I have a Bowers and Wilkins Zeppelin Air Sound dock which has AirPlay built into it. I also have an AppleTV, so I thoroughly missed AirPlay during my time with the GS3.
3. Apple - Their ecosystem and customer services is unrivaled. My phone doesn't work, or I can't figure something out... There is an Apple Genius to help me without judgement. If my phone breaks (knock on wood), I can buy a new one for $199.99 by trading in my damaged phone. Re-Sale Value.
Since most of my electronics are Apple products, I can go into an Apple Store, and get almost all of my answers in one place.
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Oh yea, this one is petty but I don't care...
Samsung commercials portray iPhone users as dumb, ignorant sheep. This I am not. I started with the original iPhone, Loved it. Haven't looked back.