There is a Classifieds - Sell Your Gear section in the forums. Those old JBLs could be hard to sell due to the limited market for vintage speakers. I like to use
USAudioMart (CanuckAudioMart in Canada). There is also Facebook Marketplace and certain Facebook speaker forums, or Craigslist, but be wary of scammers. You might want to ask in some vintage forums on where it's best to advertise.
Those Omegas look rather old as well, as in 1970s old. Model seems similar to the Omega 300 or Omega III. AudioKarma forum says the Omega 300 was an entry level 12" 3-way speaker. Not worth very much I am afraid... maybe $50. Looks like they used paper surrounds on the drivers, so not susceptible to foam rot, which is good.
If you're on a tight budget then try out both the JBL and the Omega and see which you think sounds better. Don't expect rock band level sound volume. With the age of the speakers I would stick to moderate volume levels so that you don't fry a voice coil and maybe damage your receiver. Selling both speaker sets could get you closer to a newer / better pair.