I guess my vote would be for houses. Apartments in The Sims 4 are barely even apartments. The only real difference is the facade surrounding each one and the restricted building tools. If we could build them ourselves outside of the shell, or even within a shell, I would probably use them. Not a fan of the Maxis made apartments, and the support for the gallery is nonexistent which makes playing them even more of a bore. Don't know if they looked at TV shows for inspiration or what, but some of the apartments are just terrible. I've never been to a single apartment complex that has 4 completely different layouts (not even talking floorplan, I'm talking size and shape) on a single floor in a single building. That's just a bad design.
Using a regular lot and the door locks gets me a lot closer to a believable apartment complex versus the tacky apartment themed lots they included with City Living. When apartments came for Sims 2 they broke the loading screen barrier, and allowed a more open area. The Sims 4 fails to develop apartments beyond their one loaded lot setup the game uses for every lot in every world. A new residential lot type warrants some kind of new functionality, or else what you're getting really isn't all that new.