The best replacement for steel frame is wood frame.

The best alternatives to steel frame are rated as following:
★★★★★  wood frame
★★★  aluminum frame
★★  timber frame
★★  carbon
★★  concrete frame
★  aluminum
★  aluminum frame bikes
★  aluminum frame bike
★  polymer frame
★  aluminum frame bicycle
★  carbon frame
  aluminum bike
  aluminium bike

Your alternative for steel frame is not listed? Suggest!
Speaking about steel frame, one probably shouldn't forget about carbon fork.

Other search terms related to steel frame and their ratings are:
★★★★★ carbon fork
carbon seatpost
You have in mind a companion for steel frame and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of steel frame in all years. Click on graph for more.
steel frame
wood frame
aluminum frame