Preliminary Comments: I'm not going to bash or cheerlead either network. I am not loyal to any one carrier and I bought both of my iPhone 4's at full retail price. I will be using them both side by side for the next week or so and then returning one of them. Without concrete data regarding which network is better in my area, using them both seemed like the best discovery tool. Similarities: There's no doubting that both phones are nearly identical. Aside from a few minor cosmetic differences (placement of the antenna notches and the lack of a SIM car slot on Verizon), they look the same. Regarding software, the only difference to note is the addition of Personal Hotspot (will talk about this later). Otherwise, if it weren't for the differences in networks, you're using the exact same phone. I love the iPhone 4, no matter which carrier it's on! Speed tests: Everyone likes to compare speed tests because it's probably the easiest and quickest way of comparing network speeds. Let's just get this out of the way: AT&T's network is much faster than Verizon when you compare them side by side in an area where coverage and signal is very good. In my area (the Quad Cities, which borders IL and IA), both carriers have very good 3G coverage. There are some dark spots on AT&T where I don't get a signal, whereas on Verizon I have not. And Verizon seems to penetrate better in buildings, including my workspace where I like to stream audio. However, most of the time, signal strength is very good on both. In my home, I am always on WIFI but it was a good place to start testing, so I turne WIFi off. 4 bars on Verizon, 5 bars on AT&T - both very steady: Test # / Carrier / Download / Upload / Ping 1 / AT&T / 3490 / 1655 / 229 1 / Verizon / 1595 / 301 / 304 2 / AT&T / 2059 / 1687 258 2 / Verizon / 533 / 304 / 235 3 / AT&T / 2294 / 1668 / 1894 3 / Verizon / 1162 / 285 / 255 4 / AT&T / 2143 / 1642 / 263 4 / Verizon / 1130 / 365 / 300 I will throw out the two anomalies, which were 533 down on Verizon test 2, and the 1894 ping at AT&T Test 3. On average, I am getting 2-3 mbps downloads on AT&T and just over 1 mbps downloads on Verizon. On average, I'm getting 1.5 mbps uploads on AT&T and 300 kbps uploads on Verizon. Pings were surprisingly very similar. ANALYSIS: AT&T is much faster in overall throughput, though 1 mbps download is plenty fast for just about everything except HD video streaming. Upload speeds are also faster on AT&T, though normally this is less important. Webpage Loading: Now what everybody really wants to know is how they perform when doing real-world things like loading webpages. So I sat them side-by-side again and starting loading up a variety of websites - both mobile and full. I made sure to include sites that had not been previously loaded on either device. ANALYSIS: In almost every test, there were two noticeable trends. 1) websites typically starting appearing first on Verizon, and 2) websites typically finished loading first on AT&T, particularly full sites. With mobile sites and lighter websites, Verizon had a slight advantage as the websites would actually start to appear very slightly sooner. On heavier sites, AT&T would finish first (sometimes MUCH sooner) while Verizon continued to load. So in actual practice, what does this mean? It means there really isn't much difference between the networks when loading websites. Even during those times when Verizon was still loading, typically almost everything was already visible and it was just finishing loading some images, etc. Youtube: When viewing Youtube videos, I had to test with both the included app and the mobile webapp via Safari. With the former, there really wasn't a whole lot of difference as the video is usually downgraded to lower bitrate and more compression. Both AT&T and Verizon performed well here, and video quality was decent but not exceptional. When using the Youtube webapp, you are given the option of turning on HD mode which makes the videos look considerably better. This is where AT&T threw down the gauntlet and made Verizon squirm. In almost every case, the AT&T video would start playing almost immediately and the buffer would fill much more quickly than the play rate. Conversely, the Verizon video would often take MANY seconds to even start playing (a circular hourglass would appear) and once it did, it often stopped and had to re-buffer during a video. ANALYSIS: If you plan to use 3G to do a lot of streaming video, then AT&T has the clear advantage. For light streaming, Verizon will be fine. Of course, if you are on a capped data plan on AT&T, those HD videos will eat through a LOT of bandwidth, so keep that in mind! On verizon, you won't get great HD video streaming, but you won't have to worry about bandwidth (until they start throttling you if you are a heavy user, however). Calls and Coverage: Of course, this is going to be highly dependent on your location. I use Google Voice for calls and texts and have not run into any problems using it with either device. Quality seems identical. As I mentioned, there are a few trouble spots in my area on AT&T where I don't get a signal. And in my workplace, I have noticed AT&T dropping down to Edge several times when I am streaming audio while working. Sometimes this requires me to restart the audio. I have not had that problem on Verizon as it gets a decent signal even deep inside the building. If I were in an area with poor AT&T coverage, then the decision would be easy and I would go with Verizon. But with just a few trouble spots and overall good coverage, the decision is harder. Carrier Plans/Differences: Here are the major differences I've discovered when comparing both phones and carriers: - AT&T has better throughput, including the ability to stream HD video quite well. - Verizon has slightly better latency, which translates into slightly quicker network starts - AT&T has simultaneous voice & data which is nice when looking things up or using navigation - Verizon has more consistent coverage with fewer deadzones and better building penetration (in my area) - AT&T has rollover minutes and the recently announced mobile to mobile on any carrier feature if you have an unlimited text plan - Verizon has unlimited data for new and existing subscribers (for now) - AT&T has grandfathered unlimited for existing (but no tethering) but has a 2GB cap for new (or tethering users) - Verizon has the Personal Hotspot feature with 2GB of data, AT&T has not announced it for iPhone yet - If AT&T does get Hotspot, you'll be able to use 4GB of pooled data for phone and tethering CONCLUSION: The conclusion is that I still can't decide which phone to keep and which one to return! I am definitely going to want tethering because that Personal Hotspot feature is awesome! So when comparing the two, the main differences lie between AT&T's faster network, and Verizon's better coverage and data/tethering plan options. But then there's also long-term prospects. All indications point to an iPhone 4S/5 being released this summer like usual. But we don't know if it will be on both carriers, or if Verizon customers will have to wait? And while it will probably be HSPA+, it will almost certainly NOT be LTE. However, LTE is probably coming sooner to Verizon customers than AT&T, so when the iPhone 6 comes out in 2012, I'm thinking Verizon customers might have an advantage. I guess the best thing (as a frequent upgrader who almost always wants the latest thing) to do is NOT be loyal to any one carrier and just buy your phones off-contract. In this way, you can just upgrade anytime you want and switch carriers if you need to. Given that iPhones resell for a pretty good price, you can normally get a good portion of your money back anyway (though we don't know how well the CDMA version will hold up in resell value). All in all, I'm just going to continue using them both a while longer. If AT&T announces the Personal Hotspot with the iPhone 4 and 4Gb of pooled data, that just might tip me towards the AT&T side. Hopefully, we'll find out before my 30-day return window is up!