The best replacement for simplenote is evernote.

The best alternatives to simplenote are rated as following:
★★★★★  evernote
★★  google keep
★★  apple notes
★★  plaintext
★★  drafts
★★  vesper
★  springpad
★  byword
★  workflowy
★  nvalt
★  notesy
★  onenote

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

Other search terms related to simplenote and their ratings are:
★★★★★ scrivener
★★★ notational velocity
★ nvalt
You have in mind a companion for simplenote and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of simplenote in all years. Click on graph for more.
simplenote
evernote
google keep