My upload speeds on AT&T always sucked on my XSM. Since switching to Verizon they are way better. 30-60Mbit/sec UL on VZW is not uncommon.
In general, AT&T often has faster peak DL speeds than Verizon IMHO (AT&T customer for 20+ yrs, VZW for 3 months) but Verizon is much more consistent.
I had a similar experience in my area when switching from AT&T to Verizon, but with 3G.
While the download speed was usually really good, the upload speed was horrible on AT&T with 3G, but when I switched to Verizon, the upload speed improved a lot, while the download speed dropped.
AT&T's horrible upload speed was really apparent when I was using the original iPad as a phone with VoIP for a few months in between iPhones. Download speeds were great, but upload made calling people hard sometimes.
My wife made me switch kicking and screaming.
I ended up switching to my wife's Verizon account, she was just a GF at the time, but it was AT&T's customer service that influenced me to switch.
After many years of using it, my original iPhone with the AT&T unlimited plan data and (some number, maybe 250?) of text messages broke. It was the end of May, and I knew a new iPhone, what ended up being the 4s, was going to be out in a few months away.
I suspended my AT&T account for a few months, and use my iPad with 3G as a phone for those few months until the new iPhone came out.
I ordered a 4s with AT&T and reactivated my account, only for them to inform me that my plan was no longer an option, and I would have to pay for unlimited text messages for an extra $25 a month. I ended up leaving AT&T for Verizon.
But I’m thinking she was right
=
Something interesting though, I had a lot of friends and family that used Verizon, and would always talk about how good it was, which in some places it was good.
But, I never dropped a call on my commute until I started using Verizon, as there was a dead spot on my drive. Also, it seemed like in some spots, data was really horrible, but I always seem to have download everywhere with AT&T with 3G.