I used to work at autozone and have used every thing they sell. The best is the 104 octane boost and cleaner ( its the one in the black bottle not the red). I used it in my truck about every oil change or when i need a boost. Its the only one where you can actually feel a difference. Lucas is big but i never really noticed much of an improvement, but i have a carburetor too so that might make a difference.

 

B-12 or Seafoam is great. To keep eveything slick though, I put a half quart of 2cycle oil in the gas every other tank or so. Keeps things lubed up and reduces cylinder wear.