The best replacement for quad is dual core.

The best alternatives to quad are rated as following:
★★★★★  dual core
★★★★  duo
★★★  dirt bike
★★★  thruster
★★  core 2 duo
★★  crew cab
★  dual
★  intel quad
★  i7
★  duo core
★  tetra
★  grizzly
★  atv
★  brute force
★  yagi
★  tricopter
★  mariah
★  heli
★  6 core
★  side by side
★  dual channel
  dual processor
  i5
  paraplegic
  six core
  i3
  duo processor
  plane unity
  inline
  extreme
  tri fin
  amd quad
  crew
  amd
  dual channel memory
  core 2
  rg6
  quad core
  dual gaming
  yamaha grizzly
  dual for gaming
  para
  core i3
  intel i7
  hex core
  phenom
  rincon
  intel i5

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

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



Google Trends

Scale is based on the average worldwide traffic of quad in all years. Click on graph for more.
quad
dual core
duo