I'm in China and using both giant network China Mobile and China Unicom. China Mobile signal is very great and all over the country, their service prices are cheap as well but there is no 3G network with China Mobile. China Unicom is the second giant network over here right behind China Mobile, their network coverage is garbage, signal drop or lose everywhere, in the subway, in the super market, in the wall mart, in the elevator, when you are too far away from the town you practically have no signal. Their services are cheap as well and they provide 3G network with acceptable prices.
Despite the fact that China Mobile is lacking 3G network till date, China Mobile is my ultimate carrier which i use when it comes to phone calls and sms, I use the China Unicom sim only because of the 3G network which i can access only when i'm basically under the sky, once i go inside an elevator, or inside a Starbuck i'm out of signal, the rest of the time, when in the car and stuck in the traffic, i sue the 3G network to stream international radios and that's it.