Hustler,

A Stocks and Shares ISA, selected via Fidelity's fund supermarket, has the potential to give much better returns than any cash ISA.

Example - In 2011-12 tax year just finished, Fidelity's fund supermarket reports on the dashboard that I made 12.9% (tax-free due to ISA wrapper) gains on one of my ISAs which consists of two carefully selected funds of high-growth economies.

It's risk and reward. There's also the potential to make a loss, such as some volatile funds lost 30% one year only to bounce back 40% the next year. You hope that by keeping the fund in the medium-term any losses from a previous year are cancelled out by gains in the next year, although it's not that simple.

A cash ISA is very stable, but LOSES money every year due to inflation (at least in the current UK market with extremely low interest rates).