The best replacement for mifi is wifi.

The best alternatives to mifi are rated as following:
★★★★★  wifi
★★★  usb modem
★★  aircard
★★  overdrive
★★  phone hotspot
★★  iphone hotspot
★  fivespot
★  tethering
★  dongle
★  3g for ipad
★  tether
★  hotspot
★  cradlepoint
★  usb dongle
★  verizon mifi
★  personal hotspot
★  cable internet
★  portafi
★  overdrive pro
★  jetpack
★  mobile hotspot
★  5 spot
  iphone tether
  satellite internet
  air card
  smartphone hotspot
  aircard verizon
  4g ipad
  jet pack

Your alternative for mifi is not listed? Suggest!
Speaking about mifi, one probably shouldn't forget about ethernet connection.

Other search terms related to mifi and their ratings are:

★★★★★ ethernet connection
unlimited plan
You have in mind a companion for mifi and it is not yet here? Propose!

Google Trends

Scale is based on the average worldwide traffic of mifi in all years. Click on graph for more.
usb modem