The best replacement for companions is dark brotherhood.

The best alternatives to companions are rated as following:
★★★★★  dark brotherhood
★★★★★  thieves guild
★★★★★  college of winterhold
★★★★  silver hand
★★★  fighters guild
  imperial legion
  dawnguard

Your alternative for companions is not listed? Suggest!
Speaking about companions, one probably shouldn't forget about fire and sword.

Other search terms related to companions and their ratings are:
★★★★★ fire and sword
★★★ becoming werewolf
★★ becoming a werewolf
★ werewolf
You have in mind a companion for companions and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of companions in all years. Click on graph for more.
companions
dark brotherhood
thieves guild