In terms of cost and convenience.

1. No foreign fee credit card. (Use anywhere, no fees)
2. ATM (Widely available, no fx but a service charge)
3. Travelers Cheques (1 yen per $ fx plus any upfront fees, fewer places to cash)
4. Most other credit cards (3% fee for using overseas)
5. Cash (3 yen per $ on the fx, need to exchange a bank, hotel, etc).