the front sprocket is less labor to change. Some say by putting -1 in the front is bad because its such a small turning radius for the chain. I think as long as you take care of your chain you'll be ok.
I did -1 Sprocket specialist and I liked the change in the lower RPMs. It gives a little more torque feeling down low without sacrificing to much top end. They use to sell some decent kits on ebay awhile back for like $150 for 2 sprockets and a X-Link chain, but Haven't seen them in awhile.
Vortek aluminum sprockets are cool, but some say the aluminum wear a lot faster and even break. Once again comes down to how you take care of the chain and if your riding hard (like at the track).
If I were to get a rear - I remember seeing sprockets with steel teeth and aluminum center (best of both worlds).