Anything with low charges (zero) and easy withdrawal. If you're unsure there's nothing wrong with cash accounts untill you see something that suits your investment needs. The Best Buys section probably contains a definitive listing. I hear good things about a number of Rabobank funds, both in terms of their performance and their low charges, though I've no experience of them myself.
I don't really see much difference between the rates on offer between all the banks, .25% on a monthly saving scheme really doesn't amount to much, especially if you're getting charged to transfer money from one account to another. Just be sure to avoid fads that charge you sky high fees.