If you want pure performance then road magnet is the choice hands down. You will need upgraded shocks and struts though, if not at first, soon down the road. I had road magnets paired with mazdaspeed accessory struts and the rears are completely shot; out of the car they took more than a minute to rebound. I now have them paired with Koni yellows and they are the sh!t.
I can't make any comparisons to Sportlines but I have had Prokits. The Eibachs ride smoother, and paired with my mazdaspeed shocks/struts, they were the perfect balance of mildly sporty and comfortable.
I would recommend the road magnets to anyone, but you really need to be aware of what you are getting into with this setup.