Roger, that's interesting, that you do well with spinach and ok with peppers. Those 2 seem to be the ones most people have trouble with.

I tried rock wool when I 1st started, and I didn't pre-treat it for PH. So, I have a bad opinion of it (even though it was my fault )
I have used it since, but I think sometimes it stays too wet (not enough O2..?) and small plants seem to have an issue with it.

I tried oasis horti-cubes and really like them. I use the 1x1x1 1/2 inch size. A sheet has 162 plugs. A same size ,
sheet of rock wool, has about 90 some plugs. But, the cost are about the same.

I haven't tried the rapid rooters. I'll have to check them out