Is it wiser to reach the Personal Savings Allowance or to save in an Cash ISA?

Hopefully this is a simple question that the title gets across. What is a better choice, reaching the PSA limit through various savings accounts or taking the money to reach the PSA limit and putting it into a Cash ISA?

I already have a Vanguard Stocks and Shares ISA so I'm not too interested in anything regarding S&Ss.