You seem to have your head and your heart pondering this at the same time, which will conflict whatever way you look at it.
I, and its just my opinion, would be holding on to the Apartment with a contingency fund of 6 months mortgage payments ,
Reading between the lines of your question, I would be inclined to only consider this if the Local Auth were to take on the property, and the hassle that will most likely visit you.
I think other that that, you will spend a lot of you time worrying and contemplating the worst ie: non payment of rent, disruptive tenants etc.
I have come to the realization, that your lucky if you get good tenants, but this luck doesn't last, and over time you will meet trouble. They have very little to fear, and unfortunately, as time goes by, more and more of that ilk are prepared to chance their arm.
So, in short, if you could do without grief in your life, sell.