The outside. I like it for mountain cabins and I try to use only Eaxis made fp's because Carrigon's hack doesn't work on custom. It may be crap but it's better than sticking a brick fp on a cabin. That's just...wrong.
I'm not a big downloader of CC buy/build objects, so I determined early on that I would go for as much realism as possible, but without sticking to hard rules. Consequently, most of my sim houses follow the classic hodge-podge school of architectural design, and are similarly furnished. It is likely that I would not put a fireplace on a cabin, but might install the black wood stove thingy. That being said, my beach hut (newly expanded to accommodate new spawn - yes, Alex Jolrei was born last night) still has a thatched roof and grass panel walls, but also has a black grand piano in it (don't like the silly upright thing). There are no electric lights (just the medieval candle things) but there is a fridge. These anomalies I find mildly amusing and not annoying at all.
Sims not using the fucking back door I just installed, but walking out the front door and going all the way around the house to get to the beach - that annoys me.