Best Data Reception Sim Card

Good afternoon, I like to first start by saying thank you for help I've learned while reading the message boards.

My son is going to Japan in July, he'll be using an AT&T unlocked iPhone 4. I would like your opinion on which service would be best for renting a Sim card while in Japan for approximately 2.5 weeks. I'm looking at either JCRCorp or Global Advanced Communications.
I like the features of unlimited data, as I would like to be able to talk to him on the phone using Google voice or Skype.
Which of these two services would be best for their reception while using their data program? Cities he will be going to are Tokyo 7 days, Kyoto 3.5 days, Koyasan 1day, Hiroshima 1 day, Osaka 4 days.
Global advanced Communications seems to be cheaper especially while talking on the phone ( no data). But JCRCorp has a 800-number its easy to communicate with them for general questions and they advertise that they have the best communication system in Japan.
Thank you again for all your help, coming from a concerned father.

It seems that both operate on the Docomo network so there will likely be no difference in coverage between the two operators. I'd shop more on price and features.

Here is a little more information, I found out.
Global Advanced Communication SIM card for the unlocked iPhone runs on the SoftBank network.
Renting the SIM card only from JCRCorp runs on the NTT DoCoMo on a unlocked iPhone4.
If you rent both the iPhone and sim from JCRCORP, it will run on the SoftBank Network.

If that is the case (GAC is rather ambiguious about the details on their website), then services on the docomo network will generally have better reception than those on softbank. If may not make much of a difference though if you are sticking to the urban centers of Japan.