If you're using standard consumer grade low voltage lighting, I think 12V is the market with a greater number of cost-effective products.
On the other hand, if you're looking at using high-power LEDs (0.3W-2W SMD mounted on 20mm star heatsinks, Cree, Seoul, Philips etc), a Buck driver for each cluster of LEDs should help avoid excessive voltage drop on long DC runs.
If you're using standard consumer grade low voltage lighting, I think 12V is the market with a greater number of cost-effective products.
On the other hand, if you're looking at using high-power LEDs (0.3W-2W SMD mounted on 20mm star heatsinks, Cree, Seoul, Philips etc), a Buck driver for each cluster of LEDs should help avoid excessive voltage drop on long DC runs.