I have built several buildings and have successfully imported them to UDK. When I go to make collision models of them I am presented with several choices what is the difference between all of the collision types ? I tried searching on Google and just got how the make them. I'm sure some are better in certain situations than others.
The collisions you can generate in the drop-down menu you mean?
They are pretty much what they say they are. They are for the most part collision models where all the details go in a specific direction (do you want all the edges along the Y axis? The X axis? etc.), and the numbers mean how many edges they use.
The one that stands out and you need to keep in mind is Auto Convex collision (I believe that's what it's called) which let's you specify how many collision primitives you want, how much you want them to follow smaller details and how many edges each primitive should have.
Though I do not believe you would those collisions for fracturing, do you?
The models I imported are not collision models so before I can fracture them I have to make collisions models so before I fracture my buildings I wanted to make sure that the collision models I assigned to them wouldn't have an adverse affect on performance or world interaction