If you want the Apple Inc. (Nasdaq: AAPL) iPhone 4 with the fastest download and upload speeds, stick with AT&T Inc. (NYSE: T), but if you want the best Web browsing, then it's a toss-up between AT&T and Verizon Wireless .

That's what the results suggest, at least, from mobile-device tester Metrico Wireless Inc. in its iPhone tests on live and simulated mobile networks.

When Metrico tested the two devices in a variety of markets, including congested areas such as New York and Chicago, it found that AT&T's iPhone download speeds were twice as fast as Verizon's, but the mean load time for an average Web page was about the same.

That may not be too surprising to a lot of users, as AT&T has gotten flack for reliability, not speed. When it came to reliability, Metrico found that when the iPhone is mobile, AT&T's version actually completed around 10 percent more data download sessions than Verizon's. When the phones were stationary, however, Verizon's iPhone proved to be more consistent, with a 10 percent better success rate.

Metrico isn't able to compare speech quality across carrier because of a technology bias, according to VP of Information Products Rich McNally, but it did look at dropped call rates and found that the difference was less than expected.

"The popular wisdom dictates that AT&T has a higher dropped call rate and blocked calls on AT&T iPhone," McNally says. "Our results show that, but the magnitude is not that big."

Metrico also compared AT&T's iPhone to 22 other smartphones within the carrier and compared the Verizon iPhone to 17 of its own devices. The AT&T iPhone outranked its peers in data download and upload speed, but ranked below average in Bluetooth speech quality. It came out right in the middle for call performance, beaten by top performers Samsung Electronics Co. Ltd. (Korea: SEC) Captivate and High Tech Computer Corp. (HTC) (Taiwan: 2498) Aria.

On Verizon, the iPhone was a top performer on noise cancelling, but was below average on data download speeds to other Verizon smartphones and comparable on speech quality.

Why this matters
Metrico, which does both pre- and post-launch testing, performed over 10,000 Web page downloads, ran more than 2,000 data download/upload tests and made nearly 4,000 voice calls, but it's clearly doing some fence-sitting here. That's because it's hoping to sell these metrics to the wireless operators, amongst other customers such as enterprises and device makers, so playing favorites wouldn't help that cause.

Its findings, and performance metrics in general, are important though because of the high costs associated with customer service. Wireless operators need visibility into their networks, devices and customers' experiences in order to improve them. Calls into customer-service call centers are costly and churn is even more so.

Besides providing more evidence for the AT&T versus Verizon iPhone (and soon to be iPad) battle, Metrico is also giving the wireless operators and device makers actionable data to improve their devices. For more
For more on how the wireless operator's leverage metrics, test and measurement, check out the following stories:

— Sarah Reedy, Senior Reporter, Light Reading Mobile