When learning a language you generally want to have a teach with clear pronunciation. If you're planning to learn by immersion, if it's a language spoken in several places, you want to choose the place where the local variety is spoken clearly.
For instance some people would avoid going to Australia to learn English, and Mexico is popular for learning Spanish because people "pronounce every letter", unlike say in Nicaragua or Cuba. It's easier to learn how to discern and reproduce the sounds if they are distinct. This is for adult learners. Obviously children can learn any variety.
Usually a prestige variety will be chosen for things such as news reporters, as was the case with the BBC requiring RP for presenters for many years until quite recently. But what I'm wondering is whether there are languages which don't have a "clear" or "distinct" variety like this, or for which the standard or prestige variety is not one considered to be clear.
Or could it be that it's actually all subjective and prestige varieties are assumed to be the most clear on an a priori basis?