I looked into opening a few ISA accounts recently when I was left some money in an inheritance, and one of the first ones I came across was the Premier Cash ISA from the Post Office. I remember having a savings account with the Post Office when I was a child, so I trusted them as a company that would be taking care of my money.
When I had this account as a child I do remember that everything was very slow when it came to taking money out or having interest added, but of course now everything can be done online, so I easily set up this ISA without having to visit a branch and without having to talk to anyone on the phone.
I did however have a couple of questions about my interest rate and the amount of withdrawals I could make, and the customer service team were very helpful when I needed some information about these. They guided me through how many withdrawals I could make and whether there would be any penalties to my interest rate, and how exactly it would affect the sum if I was to withdraw. I found this information invaluable as it all looked rather confusing online, so they are a great company to save with.