If your trading plan includes trading shares for capital gains over the medium term then spreadbetting is by far the best way to do it. No capital gains tax and, more importantly, no stamp duty. Also the leverage means that you can trade a meaningful amount of stock without putting up too much capital.
The disadvantages, however, are that you receive no dividends and any losses made cannot be offset against other capital gains.
Don't try and daytrade shares with spreadbetting though, you'll get mauled. In fact don't try and daytrade the UK market at all, the only place to do that successfully is the US via a direct access platform. The costs and spreads are far too high in the UK.