The best replacement for c4 is c6.

The best alternatives to c4 are rated as following:
★★★★★  c6
★★★★★  jack3d
★★★★  c3 plants
★★★  assault
★★★  c6 transmission
★★  aod
★★  c5
★★  1mr
★★  white flood
★★  cam
★★  mr hyde
★★  c5 corvette
★  cam plants
★  fmx
★  tnt
★  creatine
★  no xplode 2
★  c3
★  t5
★  bullnox
★  craze
★  m5
★  super hd
★  muscle pharm assault
★  pump hd
★  semtex
★  no xplode
  white flood reborn
  c3 photosynthesis
  no explode
  c6 ford
  cam photosynthesis
  noxplode
  iron pump
  jacked
  claymore
  501-c3
  megane
  superpump
  tko
  dynamite
  c2
  th400
  powerglide
  501c3
  renault megane

Your alternative for c4 is not listed? Suggest!
Speaking about c4, one probably shouldn't forget about no3.

Other search terms related to c4 and their ratings are:
★★★★★ no3
★★★★ creatine
★★★ super hd
★ con cret
★ d4
★ animal cuts
hemavol
You have in mind a companion for c4 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of c4 in all years. Click on graph for more.
c4
c6
jack3d