The best replacement for buildcraft is tekkit.

The best alternatives to buildcraft are rated as following:
★★★★★  tekkit
★★★★★  redpower
★★★  industrial craft
★★  thermal expansion

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

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



Google Trends

Scale is based on the average worldwide traffic of buildcraft in all years. Click on graph for more.
buildcraft
tekkit
redpower