Use them wisely and there great, manage them online and don't forgot about them, i buy everything with them, it allows me to manage my money better and get free stuff.
I have had at least 1 since i was 18 and have only paid £10 in interest in nearly 7 years and that was my own fault
I currently have
The Amex Platinum Cashback - 5% cashback for the first 3 months then 1.5% after that, not sure what to do with this now though as i am hardly earning anything but in the first 3 months i accrued £150 in cashback, used it to buy my car insurance and got £50 back just for that. Great online banking on this one
LLoyds Airmiles Duo - Earn Airmiles for all purchases, more depending on which card you use, i have 1500 airmiles now and may use them for one of them Supercar driving experiences or some wine. This one is integrated into my lloyds online so is also easy to manage online
Santander Zero - Use it in any currency for free, the rate used is the rate from xe.com which is 90% of the time better than any other rate you can get, it also saves you having to take as much cash with you abroad, me and my sister traveled for 2 months in Dubai, Australia and Dubai and used it all the time, we used internet hotspots to transfer money from our UK current accounts to the credit card account so we retained our credit limit all the time.. great card but the online system isn't great.