It's not a battle of light versus dark, it's a matter of values and beliefs - Zen-like perfection and simplicity versus nothing-is-off-limits freedom. Here's what kind of design choices that led to:
Apple iPhone 5 over Galaxy S III:
Thinner, lighter, more compact
More impressive build materials
Sharper screen with better sunlight legibility and more accurate colors
LTE on all models
Samsung Galaxy S III over iPhone 5:
Bigger, higher-res screen
NFC connectivity
Standard USB port for data transfer and charging
microSD card slot for (cheap) storage expansion
Mass storage mode, USB Host functionality
Native Google Maps
2GB RAM in some versions