The best replacement for mountain dew is coffee.

The best alternatives to mountain dew are rated as following:
★★★★★  coffee
★★★★  pepsi
★★★  sprite
★★  dr pepper
★★  crab juice
★★  diet mountain dew
★  mello yellow
★  7up
★  mellow yellow
★  red bull
★  kickstart
★  coffee caffeine
★  vault
★  sierra mist
★  coke caffeine
★  coffee more caffeine
★  mountain dew throwback
  crab juice simpsons
  mello yello
  5hour energy
  monster energy drink
  mountain dew
  coke more caffeine
  energy drinks

Your alternative for mountain dew is not listed? Suggest!
Speaking about mountain dew, one probably shouldn't forget about peroxide and baking soda.

Other search terms related to mountain dew and their ratings are:

★★★★★ peroxide and baking soda
★★ mentos
baking soda and peroxide
You have in mind a companion for mountain dew and it is not yet here? Propose!

Google Trends

Scale is based on the average worldwide traffic of mountain dew in all years. Click on graph for more.
mountain dew