I've worked with about a dozen different strains, not all of them good, but never had problems cloning. Perhaps you should be asking for proper cloning technique? I use 1" Grodan rockwool cubes, cut good hearty branches for clones, and scrape the sides of the cutting where it will be in the rockwool. I soak the cubes in a very mild solution of water and a liquid rooting hormone (Dip-N-Gro). Like a cap-full, or half a table-spoon of the stuff per 3 or 4 gallons. Keep lids on the clones, humidity needs to be high until roots begin to develop at the bottom of the cube. I put these clones under an array of Floruescent lights, water them twice daily, and they root. Every time. Only time I ever had trouble was with some spidermites that got outta hand. They swarmed the plants, I couldn't spray as there were not roots developed, and the clones all died. Balls.
Every plant I've worked with so far has been easy to clone. Mazar, Blueberry, Purple Kush, and Haze. From what I've seen, if you know what to do it would be hard to kill a clone. I've cloned without a humidity dome or heat mat with 100% success but they wilted, using the dome or being able to have higher humidity keeps them from wilting. I prefer to use a dome and heatmat though so they stay as healthy as possible. It isn't hard to clone, you just have to know what to do. Do you have a good outline on how it's done?
there are a few strains out there that dont clone very well but the majority of strains clone pretty well. Just get a decent cloning gel, I use clonex and I have 100% success every time
master kush is easy as hell. 100% success so far out of 30 clones. Even the description when you buy seeds says it's an easy cloner.
Not all strains are good for taking clones! Just because all the strains you happen to have, have a 100% success rate does not mean that all strains clone easy. Not only is it strain specific, but is also has a lot to do with how healthy the mother plant is and where you are taking your clones off of. But for the most part, all of your top notch strains from most breeders have the ability to clone very well! The exceptionally well strains usually will have a note by the breeder about how well they clone. Speed Queen by Mandala has been the absolute easiest strain that I've dealt with as far as cloning goes. And use itty53's cloning technique, that is how I do it and works excellent! The only difference is that I will soak the rockwool cubes in 5.0ph water solution for about a day before I start taking cuttings. Once I have the cutting in the cube, I will pour my rooting solution (6.0ph) over the cube with the cutting in it. To each his own though! Good Luck