The best replacement for buu is cell.

The best alternatives to buu are rated as following:
★★★★★  cell
★★★★  goku
★★★★  gohan
★★★  broly
★★★  buu
★★  vegeta
★★  gotenks
★★  kid buu
★★  evil buu
★★  baby
★  super buu
★  frieza
★  uub
★  vegito
★  janemba
★  kais
  brolly
  gohan buu
  majin vegeta

Your alternative for buu is not listed? Suggest!
Speaking about buu, one probably shouldn't forget about patrick star.

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



Google Trends

Scale is based on the average worldwide traffic of buu in all years. Click on graph for more.
buu
cell
goku