What is better poly or mono-crystalline cells?

The Silicium in polycrystalline cells is not oriented in a uniform direction, thus they have a lower efficiency, maybe 15% opposed to 19% of a monocrystalline panel. Sounds bad, right? Not really. Because we buy the panels at a peso/watt rate and that one is the same for both types. So the real “disadvantage” of a poly-panel is that it is about 20% larger than a mono-panel. But poly panels have the advantage of harvesting more energy under less optimal angles (because the crystals are facing in many directions). This is not part of the price/watt calculation and turns out like a small bonus for poly panels.
Having larger panels is for most of our customers quite welcome, because the panels shade the GI-roof, which in return stays cool and doesn’t send heat radiation into the house. Plus the roof might also last significantly longer being sheltered that way.
Therefore mono-panels are preferred for trackers (motors that let the panels follow the sun), satellites and houses that don’t have enough roof space or problems with the weight of the panels.
Recently we heard from some customers that they had bad experiences with poly modules bought from a discounter, thus preferring mono panels, but this certainly can’t be generalized for all poly modules. Ours are always grade A, despite being offered lower qualities we never imported those, because solar panels only make sense if they last.