The best replacement for viewstate is session.

The best alternatives to viewstate are rated as following:
★★★★★  session
★★★★  session state
★★★  cache
★★★  hidden field
★★  controlstate
★  session variable
★  session variables
★  cookies
★  viewbag
★  session asp.net
★  global variable
  sessionstate
  hidden fields
  postback data
  session asp net
  viewdata
  hiddenfield
  hiddenfield asp.net
  static variable

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

Other search terms related to viewstate and their ratings are:
★★★★★ updatepanel
★★★ mvc
★ gridview
★ asp net
You have in mind a companion for viewstate and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of viewstate in all years. Click on graph for more.
viewstate
session
session state