The best replacement for legos is lego.

The best alternatives to legos are rated as following:
★★★★★  lego
★★★★★  mega bloks
★★★★  lincoln logs
★★★  knex
★★★  army men
★★★  legos
★★  playmobil
★★  mega blocks
★  duplos
★  lego's
★  star wars legos
★  k'nex
  bionicles
  german legos
  duplo legos
  legoes

Your alternative for legos is not listed? Suggest!
Speaking about legos, one probably shouldn't forget about power functions.

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



Google Trends

Scale is based on the average worldwide traffic of legos in all years. Click on graph for more.
legos
lego
mega bloks