The subject says it all. What is/would be the favorite building to have on your layout? It might be a prebuilt structure or one you assembled from a kit or perhaps 2 buildings (one prebuilt and one you assembled) It might also be a building you haven't yet acquired but want to get for your layout. Be specific rather than generic - meaning list the building name and manufacturer.
Btw, if it's a building which you or someone else scratchbuilt, that'd be great to mention too. In fact, posted pictures of all your chosen and cherished buildings are welcomed.