I used both over the holidays.

My debit card, which is a Mastercard, only permitted me to withdraw $ 200 US per day at the ScotiaBanc ATMs. That's barely enough to cover the Red Stripe!

I was charged a fee of about 0.8% by Mastercard. My financial institution covered the ATM fee.

I also converted TCs at the Cambio on the road by Bourbon Beach at a slightly lower rate than cash. But I could exchange an unlimited amount at a transaction.

As MrsPurina said, TCs are getting harder to find. My Credit Union no longer carries them and the local bank from which I bought them said that they won't after they run out. But all 3 tellers at this bank said that they had not sold TCs since they had been there (up to 3 years), so maybe the TCs will be there for a while for me.

TCs just give me some piece of mind when staying at accommodations which do not have a safe.

In order to conserve cash, I also used a credit card at the Hi Lo and the exchange rate was 85 to 1 US. The going rate at the time was 90. So, there you go.