Given they are the same BTU's, they will both get as cold. BTU's is a measure of heat or heat dissapation. If an a/c cools 24k btu, then it cools 24k btu's.. Make sence? Now the type of refridgerant could make a difference, but would still be rated to the amount of heat btu's it can eliminate. I hope that makes sense.
Neither will make the outside smell. On the window a/c there is a fresh air vent, and you close that. The air that is in the room with the a/c is taken into the a/c and cooled, and expelled, so it is generally a closeded system.
Generally a mini split will be more efficient but more expensive. If your going big, get a d/c inverter high effiency mini split. will cost about 1500-2500 got a good 24k btu inverter mini split. Then there is install, some of which requires special tools and pumps. So a window a/c is the cheap easy way to go, but not as good and efficient.