The best replacement for jpg is jpeg.

The best alternatives to jpg are rated as following:
★★★★★  jpeg
★★★★  gif
★★★★  png
★★  bmp
★  raw
★  tiff
★  tif
★  pdf
★  jpg
★  png for web
★  eps
  png smaller
  bitmap
  jpeg 2000
  gif image file
  png size
  .png images
  bmp quality
  nef
  jp2
  png web
  gif images

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

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



Google Trends

Scale is based on the average worldwide traffic of jpg in all years. Click on graph for more.
jpg
jpeg
gif