There are two types of solar panels: mono-crystalline and poly-crystalline. Both technologies capture sunlight and convert it into electricity, but which is better? While each type uses silicon, there is a key difference between the two technologies. Mono uses silicon that is formed into bars and then cut into wafers, whereas poly is comprised of silicon fragments that are melted together to form wafers. The advantage of mono is that electrons have more room to move (and conduct electricity) in a cell that is made of a single silicon crystal, making them more efficient. The poly has a lower efficiency rating because the electrons have less room to move, since there are many crystals in each cell.
Mono panels are more expensive and more efficient (by 10 to 15%), while the opposite is true for poly: less expensive and less efficient. However, the gap is narrowing as technology advances. Poly is becoming more efficient and mono is decreasing in price. One factor which seemingly enables the poly to gain ground is that its cells are square as opposed to the cells of mono that have rounded corners. Thus, the poly has more surface area to generate electricity. However, because of their lower efficiency ratings you will need more surface area (roof/ground) to produce the desired amount of energy.
In the estimation of some, the panel manufacturer is an even more important consideration than panel technology. With panels warrantied for 25 years you want to select a company that is established and stable. Regarding technology, perhaps its best to say that one-size-fits-all does not apply when selecting solar panels. One must consider the project, budget, aesthetics, and the manufacturer.