No Body knows really- Slicing gives you a Good creds income at higher levels, But you never know investigation might bring back very rare mats that cost shit loads in the later game
Like MorTvicR said, as of right now you can make a fairly decent amount with Slicing, but I'm assuming when there are more people at max level looking to gear themselves out, some of the rare mats you get from other professions might jump ahead. I guess we will find out in the near future.