This is a great little place. I stayed here for two weeks after extending my 4 week stay in apt 1 (a studio on the second floor/above this one), and apt 1 wasn't available for that time—see my review there for more info about the generals of this location.
Differences between 1 and 3 are that 3 is much bigger, with a bigger shower, and has 3 beds instead of 2. It also stays cooler and is darker than the upstairs studio which is very well lit via sun exposure. Other than that, they are very similar. The construction of the buildings seems very solid—I didn't really hear the people staying directly above me at all.