Is Lissandra Top or Mid?

Its just who she is gonna be fighting really. Top is safer due to her short range but incredible escapes. Mid puts her monster ganking to better use.

she's an AP fighter really so she can either go mid (with her lower bust dmg but better sustained dmg) or go top and poke, build a bit tanky, and still make "the plays" i like her in either lane

I'd personally run with her mid, as she's a pretty powerful mid-game champion and a massive asset in team-fights. Which is handy for dragon fights and roaming to other lanes, 2 things she has more issues really using if she's put top. Especially considering most top-lane champions are sustain monsters, making them fairly difficult to push out of lane. Most are rather resilient to burst as well, which makes it doubly hard to really leave top lane without your tower suffering serious pain.

That said - if an assassin is sent mid you're going to have problems. They tend to counter mages in 1v1 situations (inversely they're also pretty screwed by AoE CC when it comes to group fights - so good news for the Ice Queen if you're jungler is going to be active in mid lane).

Mages top lane, at least ones with decent mobility like Lissandra, tend to fair OK against the common fighter/tank picks that go there though. Usually you won't have a whole lot of kill potential against them, but you can often whittle them down from a safer position than you can assassins. May not push them out, but you can prevent them from getting CS and really being much of a factor mid-game.