Wow that’s a big question and I bet you will get loads of different answers. From my point of view I would normally use HSS due to the lower cost, the most I normally make of anything is about 6 to 10 off’s. However if you are cutting hardened steel or some of the more exotic materials then carbide is the only answer. I also use carbide where cutter rigidity is required, maybe because of the length of cutter relative to the diameter. On the other hand if there is any question over the rigidity of the job or the clamping of it HSS is better, since carbide will not flex at all it will break. In short there is no right answer as to which one is better, you have to judge each job and then chose the best tool for the job.
The simplest things confuse the cleverest minds