Trying to educate myself on hearing protection. I'm ooking for a comfortable ear plug that will allow me to hear the radios while filtering out the bad stuff. Cost, ease of use, cleanliness and re-use are all factors for consideration.

How do I know what size my ear canals are, is it just trial and error and what has worked for you?

It depends on what frequency you are trying to block.  For my wife, I use .45 auto shell casings.  For the aircraft, any of the foamies are good.

I usued them for nearly 40 years flyig both fixed and rotory wing.  If you feel like you need more than that go to molded plugs.  Most gun shops sell them and they are the most effective ear protection I've used.

A wet finger

Mack's. on line. different sizes, sm, med, lg, dumbo, etc. work great. Use them for shooting, flying etc.

Isotunes.

I fly a butt fan, but it's still flying.

Custom musician's ear plugs from Sam's Club or Costco, they should be about $120 and will last for 10+ years. Get the 15 decibel filters. Or go custom CEP earmolds, that is the optimal solution for comfort and attenuation.

I second the custom molded musicians earplugs. I've had mine for about 7 years, love them. They are the -15dB filter. Use under the helmet or on the ramp whenever it gets noisy. Takes about 5-10 sec to put them in, always in my pocket and ready to protect my ears. Easy to talk to others, have a conversation, and hear the radios when flying. The HEAROS look like a good way to try a musicians style plug at a fraction of the cost of custom molded. 

I purchase Light Industries Ear plugs, soft foam bright orange ones.  These are rated at 33db noise reduction and should work well.  For the best protection, get a Dynamic Noise Reduction (DNR) or more commonly known as an ANR (automatic noise reduction) system installed in your helmet/headset for the best protection possible. I developed a 40% hearing loss while in the army in 1981 and started using ear plugs to save what I had left.  Retired in 95 with no additional hearingn loss.  Added an ANR to my fixedwing flying and installed an anr in my flight helmet in 1993 and in every helmet I purchased since then. Still flying and keeping my hearing.  Shop around for anr systems, Bose, Lightspeed, and Hedsets Inc.  Best I have had for rotarywing is the Lightspeed system, worst was Headsets Inc. system.  Bose is good for me in fixedwing and Lightspeed for helos.

Hope this helps:  Still rearing after 57 years in the air!@

The higher frequency hearing loss is related to engine and transmission harmonics not totally caused by decibels.  Some people are more susceptible than others.