Every Cash ISA allows tax free savings each tax year, but other features of a Cash ISAs vary between providers, including:
Minimum deposit - some providers have a minimum deposit of just £1
Interest rates - generally the higher the minimum deposit and the tighter the restrictions, the better the rate
Access to your cash - some cash ISAs offer instant access, others have notice periods
Fixed rates - these usually offer the best rates, if you can lock your money away for a period of 1-5 years
The interest rate and restrictions will vary from one account to another, so shop around and use the tables to make a Cash ISA comparison and find the best one for you.