They are both good options. Most 403b's I've looked at that offer a choice between the two seem to have better funds offered by Fidelity than TIAA-CREF, but my wife's employer only offers a TIAA-CREF option and it is full of excellent Vanguard funds. If you want a more informed answer you might want to post the fund options for each and people will be able to give you a better idea. What you should be looking for is a total stock market index fund (S&P 500 is a good second choice), and international index fund, and a bond market index fund, all with the lowest fees.