Chakavian
Chakavian in its actual use is the least spoken Serbo-Croatian dialect, being spoken only by 12% Croats. It is now mostly reduced in southwestern Croatia along the eastern Adriatic: Adriatic islands, and sporadically in the mainland coast, with rare inland enclaves up to central Croatia, and minor enclaves in Austria and Montenegro. All areas of old contacts with Romance languages.
Shtokavian
Croatian has had a long tradition of Shtokavian vernacular literacy and literature. It took almost four and half centuries for Shtokavian to prevail as the dialectal basis for the Croatian standard. In other periods, Chakavian and Kajkavian dialects, as well as hybrid Chakavian–Kajkavian–Shtokavian interdialects "contended" for the Croatian national koine – but eventually lost, mainly due to historical and political reasons. By the 1650s it was fairly obvious that Shtokavian would become the dialectal basis for the Croatian standard, but this process was finally completed in the 1850s, when Neo-Shtokavian Ijekavian, based mainly on Ragusan (Dubrovnik), Dalmatian, Bosnian, and Slavonian literary heritage became the national standard language.