The best replacement for siri is google now.

The best alternatives to siri are rated as following:
★★★★★  google now
★★★★★  s voice
★★★★  google voice
★★★  iris
★★★  google
★★  her
★★  dragon
★★  cortana
★  voice control
★  suri
★  dragon dictation
★  siri
★  brozek
★  galaxy
★  watson
★  skyvi
★  furby
★  sara
★  vlingo
★  xmsr
★  pidgin
★  no siri
★  evi
  ok google
  google voice search
  hawaiian pidgin
  android assistant
  dragon go
  voice actions
  google now youtube
  voice command
  voice talk

Your alternative for siri is not listed? Suggest!
Speaking about siri, one probably shouldn't forget about iphone 4.

Other search terms related to siri and their ratings are:

★★★★★ iphone 4
★★★ ipad 2
★★★ uconnect
★★ iphone 5c
★★ an attitude
★★ omnifocus
★★ ios 6
iphone 4s
husband and wife quarrel
You have in mind a companion for siri and it is not yet here? Propose!

Google Trends

Scale is based on the average worldwide traffic of siri in all years. Click on graph for more.
google now
s voice