I see resemblance in how both Telenor and Zong have made their networks: multiple sites, but with less power (so that there isn't a lot of overlap) vs. Mobilink which has fewer sites but stronger power (to cover the geography).
Result? In pockets, Zong and Telenor will do well - but you move a bit to the left or right and the speed drops. Mobilink would be able to hold onto a higher speed for a longer time - until you reach the fringe.
So - it largely depends on your luck (assuming you get signals). At my house, for example, Mobilink has weaker dB relative to Zong, but has way faster speeds - I suppose it's cause of the power of the tower which lets the phone hold onto a good signal vs Zong (Telenor doesn't really work anyway) that may have slightly better signal strength but awful speeds. Both towers are equidistant from one another.
On the other hand, if a tower goes down, the area covered by Zong will probably be less affected since they have multiple towers covering the same area - just that each tower has a smaller geographic range vs. Mobilink, where a bigger region would be dark.
Think of it as one circle, and attempting to fit three hexagons (Mobilink) or 6 hexagons (Zong).
Edit: I realized this because I tested it with my wifi repeater - i reduced its transmit power and saw a reduction in my wifi speeds. When I brought it back up high, the speeds restored. Yes, wireless is more complicated than this but the principle applies... I guess.