Prepaid SIM

I’d like to have internet access when I'll be visiting Japan next month, so I was thinking about buying a prepaid SIM card? I'd like to have an idea about how much it's going to cost and some information on which prepaid SIM to buy. If anyone has bought a prepaid SIM in Japan before, I’d really appreciate some advice.

If you're going to be in Japan for under 14 days, the following are your choices. They're about 3,000 to 4,000 yen.

Prepaid SIM for Japan (NTT Communications) http://www.ntt.com/personal/services/mobile/one/visitor/en/store.html

b-mobile VISITOR SIM (b-mobile) http://www.bmobile.ne.jp/english/index.html

BOJ mobile Prepaid SIM (Beauty of Japan) http://www.prepaid-sim-japan.com/

U Mobile Prepaid (U-Next) https://umobile.jp/lp/prepaid_eng