The best replacement for seals is sea lions.

The best alternatives to seals are rated as following:
★★★★★  sea lions
★★★  marines
★★★  green berets
★★★  rangers
★★★  delta force
★★  sas
★★  delta
★  marsoc
★  swcc
★  army rangers
★  recon
★  pararescue
★  special forces
★  marine recon
  spetsnaz
  force recon
  israeli commando
  sbs
  rings
  eod
  swat
  army special forces
  pjs
  dold
  marine force recon
  stamps
  wet seals
  stickers
  viton seals
  sea lion
  air force pararescue

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

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



Google Trends

Scale is based on the average worldwide traffic of seals in all years. Click on graph for more.
seals
sea lions
marines