The main advantage of moisturizers that have SPF is that of convenience. While using a proper moisturizer and sunscreen separately will often protect the skin better, if the added inconvenience causes you to skip the sunscreen half the time, it’s better to go with the moisturizer with SPF.
The main thing to look for is broad spectrum protection. SPF is a measurement of how much the product protects the skin from UVB rays, the spectrum of light that causes sunburns. It does not measure UVA protection, so make sure you check the label to ensure that it provides protection from UVA rays (the premature aging spectrum) as well.