IMO, finger nails and bass playing don't really work well together because they don't hold up really well and having them may effect your regular fingerstyle tone. Nothing is more un-musical than catching a nail on a string during a nice soft ballad or quiet passage. Whatever strikes the string is resposible for generating the tone and if you are depending on fingernails you will be headed for inconsistancy at some point down the road, but when that occurs(not if) really depends on how burly your nails are and how soft your strike is.
A side not about the consistancy aspect: I noticed one of my guitarist friends(classical player also) had his thumbnail on his fretting hand grown quite long. When I inquired as to the reason I found out that it was a "donor" nail so in the event that he broke one he could cut it off and glue it to his picking hand. He then proceded to tell me a sick and twisted story about his teacher having to graft TOE NAILS onto his plucking hand due to unforseen breakage and apearantly this is not intirely uncommon!!
I would go with a pick!!