Swarovski 8x20 were my only hunting binoculars for many years, the quality is excellent, including light transmission.
With the Swarovskis, the focussing wheel is centered between the barrels, and can be used either right handed or left handed. This might not be the case in other brands.
In choosing between 8x20 and 10x25, you might want to consider field of view, and also hand trembling : because they are so light, any trembling is easily transmitted to the bins. It is not an issue for me with the 8x20, but it could be with the 10x25.