What do you think is the ideal Spanish version of the Bible to use? There seem to be a few out there.

Well, Dios Habla Hoy is extremely popular, though not all that accurate. The NVI (Nueva Versión Internacional) is more recent, on the level (obviously) with the NIV -- definitely better than DHH. Biblia de las Americas is very accurate (like the NAS), though it is written in Castilian Spanish, so not so popular in Latin America. Reina Valera (Actualizada) of course is classic, but no one talks that way anymore (KJV). 

I would use more than one Spanish Bible... Just as in study in English, we will generally come to more sound (and less speculative) conclusions when we have more than one version in front of us.