Get into a final salary scheme if you can - every time!
Money purchase pensions can go down as well as up! They don't just accrue interest - instead, the cash that goes in is invested on your behalf (after the managers take their fees) and the ONLY guarantee with one of these is that the managers get their money.
If the stock market goes down, so does your pension, even though most will progressively move your money to relatively safe investments as retirement approaches.