When deciding how much to contribute to any retirement plan, you must first consider how much you can afford to save without seriously compromising your lifestyle - and how much you'll need during retirement.
Once you've got that figured out, you should opt for tax-sheltered plans whenever possible. The purpose of these investment vehicles is to grow your nest egg while minimizing your tax obligations.
Tax-sheltered plans vary in terms of when and how much you'll be taxed, as well as the maximum annual contributions you can make. The tax laws can get pretty complicated, so it's a good idea to discuss your options with a financial adviser.