Out of curiosity, what part of the country/world do you live in and are you using a hardline connection to your xbox or going off of WiFi? Being in the Midwest (specifically, Omaha) it seems that many of the servers offer a strong ping for me. I'm guessing things are a little bit different on the XBOX though since I know many console games don't have server browsers and don't show you pings. Often times, you're at the mercy of the matchmaking system.
You're spot on about Siege of Shaghai though. It's incessant. That, Lancang Dam and Golmud Railway are constantly popping up. I like all those maps just fine but seems like a lot of the servers are constantly placing those on repeat whereas other maps I really like (Pearl Market, Silk Road, Paracel Storm) don't show up as often.