Please don't take offence this is just my personal opinion, but boat and helicopters are a bad idea, cant be bothered doing the rest of the vehicle types
First i will explain why the boat isn't a great idea.
Gasses build in a body if there is decomposition, making the body have buoyancy, in turn making floating zombies, also you have take into consideration the idea of not just you trying to flee a zombie apocalypse, others with similar mindsets would do the same, then is the problem of people turning while wearing life vests, more floating zombies, you also have to remember in most fiction zombies have a primitive ability to climb, anchors and other ways to get onto the deck make your boat not as safe as it should be.
THEN the major problem of survival, people are smart, maybe too smart, congregation on isolated areas such as low populated or non populated islands and lagoons will be a definite and also runs the risk of zombies, you also need a good amount of survival knowledge to know what is edible and what isn't, where you can camp out, what animals are near by etc, the last and most deadly thing about boats is if you know how to pilot one or not, remember vehicles aren't like in the movies you need to have some knowledge in boats to know how to drive one, and fuel consumption and replenishment is a problem, same could be said about helicopters.
Now for the helicopters, The make a lot of noise, they use a lot of fuel and you need a lot of training to pilot one, its easy saying "yeh I'll get a chopper and fly away land when i need to" you have to think about constant instrument observation, set a course, make sure you have the right amount of fuel, know every safe area from the zombies, know every small airstrip to refuel, then is the matter of most helipads and airstrips being in built-up areas, the middle of airports or even in the country, all 3 as deadly as the last.
Metropolis: Large concentrations of zombies, hardly any refuel points, more chance of being surrounded
Airports: Large congregation point, a lot of zed's or military, most likely get shot down or surrounded again.
Country side: best choice, but most of these small isolated airstrips are unprotected with fences, refuelling is normally easier but more dangerous.
There is a lot more types of landing zones I haven't mentioned and a lot more random things that could go wrong, personally I would rather take my chances on foot, when you think about the congestion on water and in the air when and if this hit its not worth hitting another boat of crashing into another air vehicle, i know most of this is only fiction, but i hope this helps

peace
<3 =Fletchy=
P.S. Dosent a Moped with a chainsaw on the end sound ideal? XD