The best replacement for 7up is sprite.

The best alternatives to 7up are rated as following:
★★★★★  sprite
★★★  sierra mist
★★★  mountain dew
★★  ginger ale
★  sprite upset stomach
★  sprite which came first
  sprite sugar
  diet 7up
  sprite difference
  sprite zero
  sprite sweeter
  diet sprite

Your alternative for 7up is not listed? Suggest!
Speaking about 7up, one probably shouldn't forget about panadol.

Other search terms related to 7up and their ratings are:

★★★★★ panadol
You have in mind a companion for 7up and it is not yet here? Propose!

Google Trends

Scale is based on the average worldwide traffic of 7up in all years. Click on graph for more.
sierra mist