Visa seems to be more widely accepted in the US and South America, American Express, less so. I can't speak to Europe. An ATM card seems to work well in the SA countries that I have visited recently (Brazil, Ecuador and Peru). Travelers' checks seem to be an anachronism, even in the USA.
Foreign exchange charges vary widely with ATM and credit cards. A Google search will show which ones have low foreign transaction fees.
Good ole American cash works well in most tourist areas, though small bills in good condition work best. Heck, in Ecuador their currency is the US dollar.
Yes, I have achieved work / life balance.