Hello,
You can compare the various prepaid cards in the market by visiting the credit card section of the moneysupermarket.com site and searching in the prepaid section.
It is important you consider the purpose of your prepaid card and how you wish to use it, as the various fees and charges can make it compelling to own one for different purposes (e.g. everyday spending, overseas travel etc).
Once you have made up your mind, you can then consider the options using the comparison tables.
As an example, if you are planning to travel around the world, I would look at a MasterCard or Visa (Electron) branded product due to their wider acceptance (You can use a prepaid MasterCard at more than 24 million locations worldwide, and Visa Electron in over 12 million locations), and check the foreign exchange, ATM fees and loading fees that apply to the account to ensure you are getting the best value for money. If you are travelling in Europe, then Maestro is widely accepted as well (just over 7 million locations worldwide).
Where this is less important, and you are planning for spending in the UK, then any of the cards available should be suitable for your needs, so this is down to simple cost of ownership, and possibly if you like the card design! Check the combination of initial purchase fee, loading fees, ATM fees, and possibly even individual transaction fees.