Quickly skimming this thread: Depends on choosing WHAT
Performance: Any G series Kirby
(While I personally like the G4 best, all others (5 and upwards) are too "roundish" in their design to me, G5 to Diamond being still somewhat ok, Sentria 1 and 2 going over the top = a plain "no" (look at dipping bow in the upper edge of the vinyl bumper, a "never" thing to me, added by this roundish belt-lifter crank).
Looks and feel:
Hoover Ranger series (any of them).
Drawback: The idle extra airflow around the connector (where the belt goes)
Another drawback: All Hoovers of that age have this dreadful hard-on-hard materials vibration thing (bearings, motors, plastic housings) (all Juniors, Seniors and Rangers have it)
Design AND looks and feel:
All Hoover Commercials (nice looks and colors, nice classical design)
Drawback: Only US, not available here.
Head and other lights:
Any Hoover hardbody with lights, especially the ones with back light height adjustment. Drawback: Horrible transfer of bearing vibration to outer body (see above).
Smoothness of operation (vibration free)
Volta 1970s upright with drop-in paperbags. Never seen any easier upright on that point.
Drawback: No lights, somewhat "everyday" design.
Upright cleaning while being easy on the eye and on the ears:
Any Lux 801 and up (Royal series and Intelligence).
Good lights, good looks, easy operation, a "pull" feeling, yet vibration is low.
Drawback: They aren't an upright but a canister.
Just my 2 ct.
Joe