I've been using the liquid form of weed and feed for years now. It's easier to mix and apply, especially on small areas. I use a lawn spreader and apply it with the flat side of the blade. It usually takes a couple of passes to cover my entire yard. I'm also careful to not get any in the cracks between the sod. But I've heard that there are problems with granular.
The granules tend to get stuck in the cracks, or if they do get in the cracks they tend to clog up and be difficult to remove. Liquid weed and feed is great because you can easily apply it to any area without worrying about getting it into the cracks.