It depends on the type of currency card. They all have advantages; some have more drawbacks than others if you dont' use them a certain way.
I like my FairFX card and have used one for about 5 years now with no issues, and swift responses whenever I've needed information, help or had a query with them. I am also happy that I can top up online and link it to PayPal for US$ purchases without incurring fees.
Not so much drawbacks, but things to be aware of are not to use a pre paid card as security for a rental car, hotel room etc as it is not a debit or credit card and if there are not funds in there the merchant won't be paid so a hold is usually placed on it, even if you aren't going to be spending that amount of money. Better to place a 'regular card' down and then opt to pay the debt with the FairFX
Cash Passports work pretty much the same way, but be aware of the inactivity fee. Some of them charge you a fee if you don't use it for a certain period of time and many folk have thought they had xx in their card for their next holiday only to discover it had been eaten up in fees they hadn't paid attention to.
Travelex does a good card too and there is another one, the name of which escapes me right now.