Ridge venting will give you the most vent area possible when used on a gable roof but your ridge line may not be long enough in other types such as a hip roof. In that case the square type vents will have to do but make sure there is enough of them to get acheive the 1/300 rule
The image to the left is an example of a nail-through type ridge vent that allows you to install the shingle caps right over the vent making a very neat looking roof. You can also gain a lot of vent area with a continuous ridge vent as opposed to the square type vinyl vents. You just cut the roof sheeting 1 1/2" away from the ridge on each side creating the opening for the air to get out.