When making these decisions, it also helps to ensure that one is comparing like products. While the ATM/debit card might be the lowest cost means of obtaining CASH, that does not mean that it is the best approach to paying for a weeklong stay in a 4-star hotel. As has been noted by others, the same considerations regarding payment vehicles as at home should apply: safety and security, time value of money, transaction costs, and rewards possibilities. I would far rather pay an extra 1-2% for using my credit card (some of which is offset by any mileage earned) than be robbed in a foreign country after making a large withdrawal from an ATM!
When using ATM/debit cards, I have been told that it is actually preferable to carry one with a Visa/MC logo when outside the US. If the PLUS/Cirrus network does not work (quite possible), cash withdrawals with a Visa/MC logo card will be treated as [no fee] "cash advances" on a debit card, whereas those without such a logo are left cashless. I can not confirm this network difference, but it sounds plausible.
When pinching pennies in this field, I have also noticed that calculation dates appear to vary between banks. That is, two transactions on the same date on different cards (debit, credit, whatever) may be converted at different rates, depending on how quickly the issuing bank receives the transaction from the merchant and posts it to one's account. If you really want to get into the intricacies of this business, send your resume to the Forex trading desk of a major bank.
I second Jerseyfinn's approach: make educated choices, have fun, and don't worry excessively about small differences.
My $.02 on the original question:
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1) Exchange USD to Euro in US
2) Exchange USD to Euro in Paris
3) Bring T/C to Paris
4) Use VISA or DC
5) Use ATM in Paris
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1) Poor idea
2) Discussed in this thread; probably higher cost than other options
3) Likely more costly than 4 or 5; worse exchange rate/commission and may be issuing costs in the US
4) Best choice for large transactions
5) If your bank doesn't charge excessive fees, probably the best option for cash transactions
[This message has been edited by chalf (edited 11-28-2002).]