For the most part of my RTW trip I used my visa debit card to withdraw money from the ATMs. This was by far the best way to go as my bank here in the U.K. doesn't charge for withdrawals abroad and with the exception of Vietnam, the banks abroad didn't charge me either! However, I think this is quite unusual and some people incur quite high charges using ATMs abroad so you could shop around for the best account to suit if your bank charges are high for this service. Obviously, withdrawing money in this way meant we didnt have to carry much cash around with us either.
This worked for well for us throughout India, Nepal, SEA, Australia, NZ, South and Central America. There were a few places that didn't have an ATM machine but to be honest these were few and far between, ATMs really are everywhere these days. Most up to date guide books will tell you if there's an ATM in town and if not you can plan ahead and withdraw a bit extra until the next one.
However, that's not to say we didn't have back ups and that was a credit card and US dollars cash. You can exchange them almost anywhere and we always kept around $250 / $300 in a money belt. We hardly needed to use it but when we did, it was a just as well we had it!
If you are going to some of the more remote parts of Africa then you wont find many ATMs at all so we used US dollars again.
As for travellers cheques, we never used them. There's usually a fee to change them and they attract the worst exchange rates. The bonus is that you're covered by the company if you lose them or have them stolen as long as you remember to take a note of the numbers. Then again most insurance policies I looked at covered for stolen cash up to around $500 anyway as long as you keep the ATM receipts or bank statements.
I think most people use a combination of all or some of the methods you mentioned to try and cover all eventualities.
Hope this helps!