The best replacement for pickaxe is drill terraria.

The best alternatives to pickaxe are rated as following:
★★★★★  drill terraria
★★★★★  drill starbound
★★★★  mattock
★★★  warpick
★★  pickaxe
★★  hatchet rust
★  dragon pickaxe
★  hatchet
★  diamond sword
★  inferno adze
★  rune pickaxe
★  rune
★  drill
★  gold pickaxe
  golden pickaxe

Your alternative for pickaxe is not listed? Suggest!
Speaking about pickaxe, one probably shouldn't forget about silk touch and fortune.

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



Google Trends

Scale is based on the average worldwide traffic of pickaxe in all years. Click on graph for more.
pickaxe
drill terraria
drill starbound