Let me add one thing nobody else has mentioned: distance of stoker's nose from captain's backside. Everyone's talking about this purchase from the captain's POV, but trust me: if the stoker's unhappy YOU will be unhappy. And one of the key factors in stoker comfort is this measurement. Santana boasts about giving the stoker room to breathe something other than youir sweat, and my wife is certainly happy with our 6 year old Santana Visa.
One other thing: stoker suspension seatpost. The stoker's over the rear wheel, while you're midway between axles. So a bump you barely feel will whack her hard. And you can't dodge or loft over bumps like you can in a solo. And even a cheapo suspension seatpost costs $80--the cost ones $140 and up. If the roads you ride are smoooth, you don't need this. If they're like what we have here in California (third world), this is a must.