Not sure where I fall on this one, yet. Haven't had time to really dive into the latest revelations. Not sure who would be impeached though. None of them are in office, so it would be mostly symbolic, if even possible (not sure on the legalities of it).
That said, from what little information I have, I would certainly go with the pardon option at this point. It puts this thing to bed, at least outside of conspiracy theory, and limits the damage to our nation (much like when Nixon was pardoned by Ford). This certainly is not analogous to Watergate, as this is far beyond ordering a break-in, again from what I know. What good would come out of prosecuting? Putting a few people in jail, for crimes they have no way of committing again? Would it send a message? Sure, but at what cost? Is the message worth the damage to our "prestige"? I cannot answer any of these. Food for thought though, and things to be considered IMHO.