Ahri is a mid game champ, but very squishy. she isnt easily ganked as she has 3 abilities to either stun or get away. Swain is a late game champ, capable of soaking up damage for an extremely long period of time, and easy to snowball with. If you build swain hybrid like most people his damage wont be that much, so its up to you to decide tank, ap, or both. Cassiopeia is well rounded, but after her most recent change she isnt as micro reliant. she is probably the most skill-required of your list. Lissandra is in the same boat as swain, beefy, with good damage depending on how you build. she is mostly a teamfight champ, as her 1v1 mid-late isnt that great, but her poke is fantastic with a minion wave. lastly syndra has probably the highest damage of your list. she has the longest range stun in the game and her damage is great. her engage with her long range stun is most optimal for starting a teamfight if you have not much engage, and her ult will melt squishies. She is mosrly a 1v1 champ as her Q is a small hitbox and her ult is single target.
TL;DR go with syndra (i also play her quite a bit so maybe im biased)