Which colour spectrum?

[AC33]

I have a 20h nano and I was thinking of upgrading my lighting. I saw this fixture on sale and it fits my budget.

http://aquariacanada.com/osCommerce/...oducts_id=1032

The only problem is, I have no idea which type of bulb to pick. I have a choice between a 20k or a 10k de bulb. I was thinking of getting mostly LPS with a few SPS and a few soft corals for my tank. Anyone have any idea which to pick?

Thanks,