I've been going local and using
Ketaiya for awhile. If you have easy access to downtown, then it's a great option. You have it right from the get go with one less thing to worry about when you land. Pretty sure they would price match most competitors.
They have Softbank's 501HW which are relatively newer units that last anywhere from 10-12 hours with good range. Softbank has been solid for Tokyo, Hakone, and all the way to Okayama. Cell phone coverage is probably the least of your concerns in Japan.