OK, I'm biased but...
J3: Positive - 'Cool' factor is high. You can tool around at 60mph, door open, and enjoy the (slowly) passing scenery. They're light, offering really short-field performance and nice handling.
J3: Negative - Back seat solo. No room for even average men, to say nothing about big men (or women). Ergonomically, they suck from end to end of the flight - you can't get in, they're uncomfortable to sit in, there's no headroom or elbow room, and you can't get back out (even though you *really* want to after three hours!). They're expensive unless truly ragged out.
Pa-11: Better ergonomics than the '3, faster. Dang near as expensive as an entry-level Super Cub, though!
Champ: Positive - Speedier (less slow?) than a Cub with the same engine. Roomy! Lots of headroom and elbow room. You can actually get into one without being double jointed in legs and arms. The door opens and you step in and out. Back seat of some is huge. With the later 7EC, you have 26 gallons of gas and can carry it *and* a passenger - I'm over 180 and can carry full fuel and a 150-160 pound passenger w/o any baggage. The Champ *has* room for baggage. They're generally $6-10 thousand less expensive to buy than a comparable Cub ($16-20 less than a PA-11). Champs, especially with the Hanlon-Wilson exhaust, have heaters that actually work! Winter flying is possible and even enjoyable.
Champ: Negative - no 'Cool' factor like the Cub. Heavier controls, especially the ailerons. Longer landings and takeoff - but not that much longer. Landing gear is not as good for skis and/or rough fields. The tail is heavy, making it harder to move by hand on the ground. The whole airplane is heavier than a Cub by 100-200 pounds. The useful load is as good and usually better than a Cub, though. You need an STC (cheap!) to fly with the door off and have no way to carry the door in the aircraft, so you have to leave it at home.
Any of the 3 is a hoot to fly on wheels or skis. On floats, the PA-11 is probably the best of the bunch, with the Champ at the bottom. None is a real load carrier on floats, though.
My 7EC will land in 200 feet (if the wind, temperature, field and I are all in sync) and take off in around 300. That's at the very light end. Loaded to gross weight, you can add 200 feet to both. Still decent, though. With a C-90, 74 x 42 prop and cool air, the climb angle is pretty impressive. As one fellow said, "You've got a helicopter!" On hot days, with a load, you'll wonder what happened to the other 50 horses up front. Bill was duly unimpressed with his ride at New Holstein, I think. I did have one weak (dead?) cylinder at that time, though. I replaced it a week later, and the performance improved dramatically.
Jon B.