The Redmi 3 has been quite popular thanks to the compact body, affordable price tag and capable hardware. The Pro version costs some 30% more than the regular one( CNY899 vs. CNY699) and in return, it offers more RAM, more storage, and a fingerprint reader.
The Redmi 3s and the Redmi 3x, on the other hand, are based on a different hardware platform - they use the Snapdragon 430 instead of the Snapdragon 616 - it’s a slower chipset, but it also happens to be newer, so it has a faster LTE modem and a faster GPU. They also have a more recent version of Android out of the box - they run MIUI 7.3 with Android 6.0.1, but MIUI 8.x for the original Redmi 3’s is already in beta as well so it shouldn’t be too long until it gets updated.
The Redmi 3s is available in two variants as well - the 2GB/16GB w/o fingerprint sensor - and The Redmi 3s Prime, which has 3GB/32GB plus a fingerprint sensor. These variants cost the same as the Redmi 3( CNY699) and the Redmi 3 Pro( CNY899) respectively. The internals of the Redmi 3x are the same as those in the Redmi 3s, but the design is different( more angular, less beveled edges), and it can be purchased only in a 2GB/16GB configuration.
Speaking of purchasing, it’s worth pointing out that the Redmi 3 and its Pro version are currently officially sold only in China but thanks to grey imports, the phone can already be had in other countries and the software is already localized in a number of languages with the silent support of Xiaomi themselves.