[dheera]

I'd go for 48VDC.

12V would need some fat wiring to avoid incurring voltage drops for normal amounts of loads.

48V is nice because you can use much thinner wiring, and it's about the highest "safe" voltage to accidentally touch with normal dry skin.

[spoonjim]

48V would definitely be a big ouch or worse for a kid sticking a wet finger inside or something. 12V is completely safe in all circumstances.

[liotier]

Telco employee here... Colleague swapping a card touched 48V - knocked out for a little while, came back and was taken to the hospital for check-up and recovery. 48V at typical rack amperages is no joke.