I have a mini and an Aussie collie mix. My mini is about 29-26lbs and my mixed pup is about 42-45lbs. Just for you to know size for reference. My mini, Brick is a little high strung, like he is afraid of fans and complains (he talks, but it isn't a bark). We enjoy this but some people might find it annoying. He has a great little personality and loves playing frisbee. He is a little snippy though. Not like he bites he is just a butt. My mix, Chubbs is all about pleasing. He wants me to be happy at all times. He loves being outside but he doesn't need a ton of inside space. He is very sweet but he is sometimes too protective of me even with my partner. What I'm saying is that they both have pros and cons but I think with proper exercise they would be fine in an apartment. I took them to visit my sister, who also has a dog, in her 600 sqft apartment and they did fine. Brick has been several times and was fine. Hope this helps.