In all my articles on Jetpack Joyride, I've kind of been ignoring the elephant in the room. To whit, vehicles.
Some things are pretty obvious about vehicles: they make the game a lot easier, because you can't be killed while in a vehicle. They also improve your odds of getting more money (two free sets of coins when you get the vehicle, a third when you lose it. Plus, you can pretty easily get the big coin magnets) and spin tokens (nothing so specific here, but they seem to occur about twice as often when in a vehicle).
But what's let obvious is how they help/hinder various missions.
Certainly, as noted above, they all help with getting coins and tokens. But what else are they good for?
Well, none of them are any good for brushing the ceiling, walking, sliding on your face, or high fives. Also, none are good for avoiding coins (darned near impossible, when you have the magnet). None do anything for any of the missions involving buying anything, nor for using the Nerd Repellent.
Gravity Suit: this one is especially well suited for getting whole groups of coins (well, with the magnet), as the coin patterns it gets tend to have lots of little groups. This one is quite difficult for near misses of zappers and missiles, but can do both. For knocking over scientists, it is not very good; because of that, though, it is pretty decent for avoiding hurting scientists. For flashing lights, it's ok, and decent at going over zappers.
Bad As Hog: Near misses with missiles and brushes of flashing lights are impossible (well, with the exception that you can hit the very first light if you get Free Ride, and that ride is the Hog). It's very good for knocking over scientists (comparable to the stomper); for the same reasons, it's darned near impossible to avoid hurting scientists over any distance. Near misses of zappers are difficult. Really, the only thing this is very good at is covering distances (though that also means it isn't bad for collecting spin tokens). And it's so-so at going above zappers.
Crazy Freaking Teleporter: Godlike for covering distance and for flying over zappers. Terrible for near misses, though neither type is impossible. So-so for hitting flashing lights and for knocking over scientists. Pretty good for getting groups of coins, especially with the magnet. Also awesome for mission of avoiding touching floor or ceiling, as you can't do either in it. It's also one of the best for avoiding hurting scientists, and the only one with which I have successfully avoided grabbing coins when I had the magnet.
Mr Cuddles: Very good for covering distance and hitting flashing lights. Not very good for knocking over scientists; hence, pretty good for avoiding hurting them. Decent, but not great, for near misses of both types. Pretty good for going over zappers.
Lil Stomper: (Unrelated: the name always makes me think of "Li'l Pepe", from Romancing the Stone.) Pretty good for near misses of both types, also for hitting flashing lights. Not bad for flying over zappers. And, of course, the only one with which you can complete a mission by knocking over scientists.
Profit Bird: Best of the bunch for just about everything (except covering long distances; control gets wonky after a kilometer or so). Also not great for knocking over scientists, I suppose. But very easy for near misses of both types and hitting flashing lights (so easy, in fact, you can easily find yourself doing it accidentally). Suppose, too, not quite as good as the teleporter at going over zappers, but still better than any of the others.
So, that's the skinny (to the best of my knowledge) of how the various vehicles help and hurt accomplishing missions. Good luck.