Basically any champion with displacement ability can do it.
Once you know all of the characters and abilities this should not be a problem for you.
My suggestion take nidalee for a custom game try jumping different walls and stuff (remember to face it directly). You now know what walls nidalee and renekton can cross (maybe I missed a champion or two with similar displacement range). (or search a site like mobafire to see pictures)
Take ezreal for a custom game, try jumping different walls and things. Now you know what walls you can jump with flash, and what walls pretty much all other champions with displacement can jump. Pretty much all walls are jumpable with these types of champions.
There is really no easy/hard/extremely hard walls to jump over, you either can jump over it or you can't just get as close to the wall as possible and use your ability.
I suggest you use smart casting (shift+ ability, or rebind your keys), it saves half a second which can change affect if you live or die.
Also another things to note is that Jax and Lee Sin can jump to walls, if you have smart casting enabled it is possible to run to wall place ward and jump to it fast enough.
Use bushes to your advantage and don't act predictably. i.e. move towards their base not yours.