Aside from considering which introductory offer is more generous, the main thing to look out for when you compare credit cards is the APR (annual percentage rate) that is charged. Credit cards are regulated by the Financial Conduct Authority (FCA), which requires a clearly indicated APR that allows easy comparison between cards. This relates to the interest that at least 51% of customers will be offered on standard purchases per year. This makes it easy to compare credit card rates at a glance but remember that you may not get this rate; bear in mind too that if you're looking to use the card solely for transferring debt, you may want to look at the interest charged on that instead.
Next to interest rates and introductory offers, you may also want to look at eligibility criteria and how you can apply for and manage the card. A card that is appropriate for most people might not be the right fit for you, which is why it's so important to always compare the best credit card offers to find the one that's best for you.