I feel brakes are the most overlooked mechanism on any rig. Most OEM brakes are only halfway decent but the rest are junk. Definitely make an upgrade.
Slotted allows for better de-gassing and cleaning of the pad to remove debris if caught in between the pad and rotor. Tends to be the better choice among the three if you're looking for bite. Cross-drilled lightens the rotor and gives you slightly better bite in wet conditions. I tend to like slotted if given a choice. Look at the rotor vane as well. There are straight vaned, which can be found on standard OE rotors, and directional vaned which can be found in aftermarket. Directional would be the best to dissipate heat as it gives you a better evacuation of heat which is the braking system's worst nightmare. The most effective choice would be to get better pads with more bite. That should help the best along with an upgrade to SS braided lines. Do watch out for cheap rotors that are cross drilled and slotted. They tend to crack between the drilled portions.
As far as the SS brake lines are concerned, they will only benefit you if added. The SS braids allow for minimal expansion of the lines when using the brakes, which in turn gives you better braking response and less of a "mushy" feel. They are more expensive, but in the long run, you'll thank them.
One of the best sites in regard to brakes:
http://www.zeckhausen.com/technical.htm