The best replacement for galaxy s4 is iphone 5s.

The best alternatives to galaxy s4 are rated as following:
★★★★★  iphone 5s
★★★★★  htc one
★★★★  note 3
★★★★  note 2
★★★  s3
★★★  lg g2
★★★  s5
★★★  iphone
★★★  iphone 5c
★★★  nexus 5
★★  s4 mini
★★  s4 active
★★  moto x
★★  iphone 5
★  droid maxx
★  galaxy s5
★  iphone 4s
★  galaxy note 2
★  samsung galaxy note 2
★  galaxy mega
★  galaxy note 3
★  galaxy s4 active
★  galaxy s3
  galaxy s4 mini
  sum sung note 2
  xperia z
  xperia z1
  iphone 5s specs
  iphone 4
  droid ultra
  lumia 1020
  htc one max
  iphone 6

Your alternative for galaxy s4 is not listed? Suggest!
Speaking about galaxy s4, one probably shouldn't forget about itunes.

Other search terms related to galaxy s4 and their ratings are:

★★★★★ itunes
★★ ford sync
You have in mind a companion for galaxy s4 and it is not yet here? Propose!

Google Trends

Scale is based on the average worldwide traffic of galaxy s4 in all years. Click on graph for more.
galaxy s4
iphone 5s
htc one