if possible give me a few pros and cons for both of them
thanks alot

Swain
Pros- tanky, good damage, some descent CC, great spell vamp
Cons- blue buff reliant/ mana relaint for ult, short range
Ori-
Pros- Very fun, can be played support bot, good at initiation with ult, good utility and cc, ball is a free ward for when u support bot btw ;P
Cons- Hard to play, hard to know what to level up, hard to hit spells with

Swain
Pros - Great carry if built right; Tanky if built right, with some great burst in there; good ult with that spell vamp; Survivability for a mage is decent
Cons - Squishy if you don't know how to build; Mana-hungry early-game; slow

Orianna
Pros - Good burst if built right; Decent mobility; Can be support or full AP with her ball-thingamajiger
Cons - Squishy as HELL; big learning curve; skill shots kind of hard to place right if you don't know what you're doing

Swain - Pretty easy to use. His passive is amazing for mana, so he rarely goes hungry. His Ultimate, as well as his natural amount of health, makes him tankier than a lot of middle lane champions. Although his combos rely on a good skill-shot initiation. Very fun to use and learn.

Orianna - A bit harder to play. You have to be able to micro-manage with her. You have to be able to grasp the concept that your damage comes from one source, and your health pertains to another. She is amazing for her utility: A shield, a slow, a speed boost and a pull-and-stun. (Also very fun when you realize you can shield an ally, and while the ball is on them, activate skills off of them, even if they are out of your normal skill distance.) Harder to use and master, but helps the team a lot more, I believe.

Hope this helps.

Swain - Also, sorry to double post, but I am seeing a lot of comments about how Swain is mana-hungry or blue-reliant. This is not true at all, lol. His Passive gives you mana as you Cs and his Ultimate is a toggle (like Anivia's) so when used right, it hardly takes any mana. (The only time I ever run out of mana on Swain is when I am in a teamfight and I just sit there with my Ultimate on throwing out skills.)