Koehress seed, interested on which is the fastest growing/ easiest.
Im into ingens and canariensis, but please suggest other species.
Other candidates
euphorbia vigueri
euphorbia virosa
euphorbia zoutpansbergensis
euphorbia grandicornis
euphorbia grandidens
euphorbia coerulescens
euphorbia curvirama
euphorbia cooperi

Euphorbia ingens will fill a a 2 gallon (20cm) pot in 2-3 years. It's pretty fast. The seedings tend to have a longer lifespan in pots (compared to cuttings) before they get so huge they demand to be dealt with by use of the knife. Euphorbia viguieri is more like a crown of thorns in size and shape. E. cooperi is a monster but I think people usually grow that one from cuttings. I grew E. grandicornis from seed and it's more like a bush, in the sense of not having a main stem, rather more like a collection of branches. But pretty fast and well behaved.

In their Euphorbia catalog they also have E. susannae (not a columnar plant) which is lots of fun because it grows into a tremendous mound (but still feasible in a container) over time. Mine is in a 12 inch pot now and has maybe a hundred heads.

Like it says on my wish list(comment footer) , i want a tall euphorbia(or at least a interesting one). Some of the seeds there are expensive(resinifera,susanae).
Never had euphorbia canariensis? I heard that one, grown from seed, is used as grafting stock.

The susannae seeds are relatively expensive compared to ingens because the plant is not self fertile and you need two plants of opposite sexes to make seed. That by way of explanation so you know. In my mind those susannae seeds really are worth 5 times as much as the ingens seeds (being relatively inexpensive compared to plants, to start with). Because the plant has a fascinating form and will most likely have a much longer practical lifespan in a container.

I realize you're looking specifically for a certain type of Euphorbia, but while you're shopping the genus in that particular catalog, that's an underappreciated plant with some potential.

I have seen but not grown canariensis. That could be fun.

Im also eyeing virosa, from namib . Dont know about care, ingens and canary islands euphorbia are more straight forward durable.
its not that i wouldnt grow susanae, but im out of room for small euphorbias, need somethingt all i can manage from a floor pot, not a windowsill plant/

E. virosa is pretty seriously slow, at least compared to the other options you mentioned. It could still be in a 15cm pot after 10 years.

Hmm, il have to take into consideration that everything here is slower too. So virosa is a no-no.