Very good points by Error and Moby(via Cop). Also keep in mind, the fact that it is a demo means that it is going to be limited as to the amount of maps, game types, weapons, and other things.
Due to the mission objectives in both the R6 series and the SWAT series, it is hard to say which is better. The two types of play, while both tactical in nature, are very diferent. One is military based and the other is law enforcement based. It is like comparing apples and oranges. The two games play by a completely different set of rules of engagement. This is one reason I think I will find myself enjoying both games very much, and not trying to decide which is the better of the two.