Don't think that spending $300-400 on aftermarket ones is gonna do shit, it won't. If they need to be replaced OEM ones are good. They do work! Search Rockauto.com and other sites for good deals on them.
I ran a set of Granatelli's blue ones for about 4 years. They lasted just fine. The aftermarket ones have a lot thicker wire but need to be manually adjusted to the proper length vs. the stock ones that use a spring style wire to transmit the power to the spark plug.
After all the spark plug changes over the years since I put them in, they are just a hastle. When you go to remove the plugs the center wire sticks to the top of the spark plug and you go through the work of putting everything back in place not knowing if the manually adjusted legth wires are making good contact on both ends.
I went back to stock ford ones this past year. If one or more of yours are burnt out, I would almost suggest even getting a used stock one before shelling out cash for new aftermarket ones.