I fitted my engine in through the top and in my personal opinion it was a right ball ache, its a tight old squeeze manouvering the engine and box round past the brake servo whilst avoiding the strut top on the opposite side of the bay.

If its easy for you to get the car in the air then out the bottom is what i would do, the engine would of been fitted below from the factory, and since when have production lines employed a more than necessarily complicated method