Well, you asked for MOST comfortably ... which means there is only 1 true answer from any 1 person you ask. My guess is I haven't been in such a car because I would imagine it is something like the aforementioned Mayback or a Bentley or Rolls.
If you want something affordable that seats 5 comfortably, you want a full-size car. That would be something like a Chrysler 300, Lincoln Towncar, or Mercury Grand Marquis. For a step up, I think you have to go WAY up to the likes of a Bimmer 7-series, MB S-class, Audi A8, or Infiniti Q45.