The best replacement for illustrator is photoshop.

The best alternatives to illustrator are rated as following:
★★★★★  photoshop
★★★★★  indesign
★★★★  inkscape
★★  drawit lite
★★  fireworks
★★  corel draw
★★  freehand
★  corel
★  coreldraw
★  adobe photoshop
★  artist
★  publisher
★  sketch
★  flash
  idraw
  gimp
  graphic designer
  visio
  pagemaker
  quark
  omnigraffle
  sketchbook pro
  adobe indesign
  emblem
  xara
  in-design

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

Other search terms related to illustrator and their ratings are:
★★★★★ wacom
★★★★ transparent background
★★★★ silhouette cameo
★★★ after effects
★★★ photoshop
★★ live trace
★ vinyl cutter
★ wacom bamboo
★ indesign
★ craft robo
vector art
changing stroke
You have in mind a companion for illustrator and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of illustrator in all years. Click on graph for more.
illustrator
photoshop
indesign