when deciding between which of these states to shoot for, i can think of only two legitimate criteria. 1, how much suffering will remain and 2, what will one's impact on the world of people and things be.
the only people who can answer number 1 are those who have experienced both, and they are unanimous in their opinion that the second state has less suffering (no suffering at all rather than some suffering)
the answer to 2 can only be speculated about, but there are two criteria here as well in terms of deciding which state is most conducive to helping others gain awakening. firstly, there is the question of capability, who is better able to help others end suffering? then there is the question of inclination, who will make more effort to help others?
because people in the second state have made a full end to suffering, they can help others eradicate more suffering than those in the first state. also, as their actions don't have selfish goals, they will be acting in ways that help only the other rather than the other and themselves. people who feel compassion have some degree of personal investment in helping others because their own enjoyment is at stake, this is where we get people helping others who do not wish to be "helped."
as for who is more inclined to help others, it would be the people in the first state, as they have personal investment in the other person's welfare. (actually i don't really have any idea about the inclinations of actually free people, so i might be wrong)
all in all however, i would say that people in the second state will have a stronger positive impact, as they are the ones who can lead others to a full end of suffering rather than just a partial one. and in the case in which the person is willing to be helped the second state people will always have the upper hand. in the case in which the person in question is not willing, it's unlikely either side could do anything useful.
so that's my opinion, i dismiss any other criteria such as the "loss of humanity" i don't see any reason to assign value to things that do not help to reduce or end suffering. how inhuman of me, i know.
edit: i'm not sure if you are bringing rebirth in here or not. if rebirth exists, than the person not coming back to samsara will doubtlessly have no ability to help others come out. (my experience with parinibbana is limited

so i can't be sure)
so, in that case, yes i suppose the first state people would be better able to help, i think even in that case i would still go all the way however.
edit 2: to be totally honest, i actually only really care about my own suffering right now. i think my previous points still stand though.