The best replacement for windows forms is wpf.

The best alternatives to windows forms are rated as following:
★★★★★  wpf
★★★  web forms
★★★  mfc
★★  wpf application
★  win32
★  windows presentation foundation
★  wpf performance
★  xaml
★  wpf 2010
★  asp net
  winforms

Your alternative for windows forms is not listed? Suggest!
Speaking about windows forms, one probably shouldn't forget about xna.

Other search terms related to windows forms and their ratings are:
★★★★★ xna
★ wpf
You have in mind a companion for windows forms and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of windows forms in all years. Click on graph for more.
windows forms
wpf
web forms