The best replacement for winforms is wpf.

The best alternatives to winforms are rated as following:
★★★★★  wpf
★★★★★  webforms
★★  wpf performance
★★  windows forms
★  mfc
★  gtk#
★  gtk
★  wpf application
  wpf 2010
  web forms

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

Other search terms related to winforms and their ratings are:
★★★★★ mono
★★★ mvc
★ mvvm
You have in mind a companion for winforms and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of winforms in all years. Click on graph for more.
winforms
wpf
webforms