Actually, none of those canvases have been discontinued. They are all still available-- just not in the US market. Daguerre and Monet are they only Hahnemühle canvas sold in the USA. Choosing between those surface really depends on the types of images your are making. A surface like Monet or Canvas Artist seems to work better with images or photographs that have a more painterly feel. Where something like Daguerre would work better with a more photographic image. Canvas Artist is a matte canvas, that the most 'organic' feel to the weave, and the warmest white-point. Followed by the matte canvas, Monet, which has a similar warm whitepoint and organic texture except the surface is more even and smoother than CA. The final matte canvas you listed, Daguerre, is which has the brightest white-point of all the canvses in the Hahn. line. It also has the finest and sharpest texture of the matte canvases, which suits it to reproducing crisp photographic images.
The Goya has a beautiful satin-finish with a warm white-point similar to the CA. The surface texture has an organic feel to the weave and a gesso-ed appearance like CA and Monet. The Leonardo has a very high gloss and a bright-white point. The surface texture is a fine precise weave close to that of Daguerre. IMO it is the best high-gloss canvas on the market. You really get a great Dmax, and they designed the texture just right so the gloss does not detract and get that distracting light-scattering that other high-gloss canvas suffers from.
They are all Poly-Cotton except Monet which is 100% Cotton. As for weight/ thickness/ rigidity, I would say the CA is the thinnest lightest weight and the most flexible- it really feels like fabric. Goya is similarly light in weight and thickness, but is a little more rigid from the satin-gloss coating. To the touch Leonardo feels the stiffest, I think because of the high-gloss coating. But actually, Monet is the thickest and the heaviest gsm.
If you want a glossy canvas Goya and Leo are great because because you do not have to varnish. But if you want to more control of how much gloss your print has, you are better off buying one of the matte canvases and varnishing it your self. Hahn. offers a great varnish-- that I use alot. It really lets you control how much shine your print has. The more coats the glossier the print. Whew, thats alot of info-- I hope it helpful.
Good luck in finding a canvas!