if you want to choose the strongest one, wait for naruto, but if you play this game for fun, and sasuke is your favourite character in the anime, buy sasuke (naruto stronger than sasuke in this game)

Rinne Sasuke is joke in Naruto Online, maybe for Ranked battles but in 1v1 its not worth to got him just for % chaos and steal chakra when somebody hit him.

or i should pick konan?

Imo, prices are nearly same and depends which events would be that week, if you are lucky you can get Fukurokumaru event + Naruto Six path claimable like in Lucky Throw thats probably best way how to get tons of items for free + your ninja.

But still Naruto can handle a little more than Konan he is more flexible and dont need too much support ninjas around him.