So, I'm looking at getting all three of these champs eventually, but for now, I have to pick one. I need a good mid laner that can stand up to mages with targeted abilities and not die, but I also need good sustain tops.
Anyway, which of these three champs would be the best for what I described above?
Also, not related to the topic, what are some good, tanky champs that are versatile enough to top or jungle?
Kassadin has been a bit under the water lately. Not saying he is shitty, but from all the things you hear going around ; He is not a safe bet you would want to go with in the mid lane as you would have to exert tons more effort than many other champions to use him at his best, and even then you may have issues.
Vladimir is more of a top laner I would say and he has a somewhat weak game until around level 7-9, but he has great sustain since he uses no resources and can heal himself with his Q and W along with his E (doesn't heal) which can amplify his self healing, spell regeneration and spell vamp, and he can wind up being hard to kill as the game goes on. His W makes him untargetable as well which gives him a boost to his ability to survive. His R can do wonders in team fights as well.
Fizz has in his own way, much higher survive ability due to his E making him both untargetable as well as boosting his mobility to insane amounts (even some point and click abilities have a travel / cast time) and his sustain will mainly come from the 
which is a common item pick for Fizz, but his sustain can be a bit iffy depending on who you are up against. With further cool down reduction as well as levels, his mobility and power to survive is off the charts to the point where it is toxic.
As for the Top lane / Jungle 
can turn out to be very nasty, but you didnt hear it from me
I would say Fizz. Vlad is a top laner, he is at his weakest early game and any poke mage will make his life hell. The only time you would take him mid is against assassins who have to whittle you down with poke (so any but Zed) and he can puddle their burst.
Kassadin isn't very strong right now. Hes not terrible, but not great.
So I would say Fizz. Troll Pole gives you great safety from point-clicks (I imagine you mean Veigar?) and ganks. Insane burst, decent roams, gets a lot out of Sheen and has an innate counter to Vei burst.
And as for Top/Jungles I suggest Olaf, Voli, Maokai, Shyvana or Tahm.
Vlad. Just play like a bitch. Don't even poke, just play like a bitch. Forget about AA's, just use q to last hit minions. Enemy poked you? Just suck some blood. Enemy come near you or getting ganked? Pool, niggga, pool.
Seriously though, Vlad is probably the easiest. All you have to do early game is farm, and late game you become a monster without having to do much. Fizz is really strong too, but he has no sustain. Doesn't matter when you kill everyone instantly though. Never played Kass but I'd say he's the hardest.
I love all three but kassadin is in a rough spot right now I think. You almost always have at least two to four tanks running around now a days. None of the tank buster items synergize on him. Whats thepoint of deleting the adc and maybe the assassin if you cant do anything to the rest of the team.
That and he has a really hard start compared to other mid laners. His e is really situational until 6. You really have 2 skills until things get rolling in lane and that sucks so much if you are fighting someone like yas. He can just walk up to you pre 6 and poke without spamming his e so you dont get stacks.
Fizz. Just start flask and pots, win game.
Also, not related to the topic, what are some good, tanky champs that are versatile enough to top or jungle?
Cho'Gath, for sure. He has great sustain in the jungle, great clear speed, great ganking, and resistance to invades. A lot of people go cinderhulk, but don't realize that his Feast stacks count as MAXIMUM health, and not BONUS health, which is what cinderhulk scales off of. What you really should be doing is going Devourer. A super high base AD combined with Vorpal Spikes and the Devourer passive makes his auto's do a lot, so the attack speed gained from Devourer really increases his damage output. Not only that, but after the 5.13 AP items rework, Rylai's Scepter now makes his E slow for 40% instead of 15%. He's just a walking death machine mid to late game, and if you walk into him, you'll be silenced, perma slowed, chomped on, and beaten to death with auto attacks.
Definitely give him a try. If you want to know more just give me a reply.
