Eric, I think it's mostly a matter of what you like. I'm kind of a use what I got kind of person, so I have many different materials for my raised beds. To be honest the double concrete is my favorite. I dug down a couple of feet and placed concrete block around the hole I dug, two high. I filled it hugel beet style. I love it, it is so much easier to work on. Honestly I didn't level it except enough to keep it from having any large gaps. I started out using weed cloth to keep the weeds out and the soil in. I didn't use it this last time, and didn't notice any soil escaping. I did lots of research, and considering my blocks are super heavy I think they are made with concrete, and not cinderblocks. I guess there can be a problem with lime leaching into the soil, but if this is the case, I haven't noticed it. What I like about using concrete blocks is they are cheap and last a very long time. They don't have to be ugly. You can paint them, or plant something around them. I didn't bother, because my eye is always drawn to what is in the bed, and I don't think I have ever thought that is ugly. You also have options as to how you put them together. I have made a star shape, flower shape by putting the blocks together corner to corner instead of edge to edge. I don't have one like that at the moment, but I like the way it looked, and never had any problem with them coming apart.
An other bed is also a hugel beet and dug deeper because I didn't have enough blocks to do a double wall, so it is only one block high. It works just as well, just lower to the ground. I don't know about others, but I tried to grow things in the holes as bonus space, and never could keep anything alive. Maybe because the California sun makes it too hot and or dry? The one block system shows even more garden and less block if you find them unsightly.
I built a raised bed for my flowers 3 years ago out of cedar fence posts I got on clearance at Home Depot because they had some cracks and some weren't straight. The hole project cost me less then 10.00. I spray painted the outside to help it last longer, and because I had it, so it didn't add to the cost. I also lined it with weed cloth so I didn't need to worry about soil escaping through the knot holes and gaps. I love it and it seems to be holding up well. (I took a picture, but am embarrassed to share it. With my husbands health problems, the holidays, and just general laziness, I'm so very behind on all my fall and winter projects.)
I also have two 4'X4' raised beds that I got on clearance several years ago. I didn't like them because they were only about 6" deep and that just wasn't deep enough, so I bought the cedar fence boards and added them to the top of the raised bed, and it worked so much better, and has lasted several years.
Last my niece was taking a wooden twin bed frame to the dump. I asked her if I could have it and unpainted and untreated it lasted about 5 years. It finally fell apart this year. I will replace it with concrete blocks mostly because that is what my son got me for Christmas, but I'm not sorry I used it. It was a perfect size, free and kept it out of the land fill. Basically you can make anything work. The cement blocks will out last all options. Good luck to you, what ever you decide will be great, because lets be honest its really about what is inside that matters the most. Happy Gardening.