Hard to give a single answer without more detail - are you over 50; do you pay tax; do you want instant access; do you want a cash card; can you lock the money away for a year or more; how much have you got to invest; do you want a regular saver - x amout per month?
Lots of impartial advice and the best rates here:
http://www.moneysavingexpert.com/banking/
And listen to today's Jeremy Vine show on Radio 2 on the internet radio 'listen again' - about one hour in to the show.