Varieties of Chinese

Mandarin
This is the group spoken in northern and southwestern China and has by far the most speakers.  This group includes the Beijing dialect, which forms the basis for Standard Chinese, called Putonghua or Guoyu in Chinese, and often also translated as "Mandarin" or simply "Chinese".  In addition, the Dungan language of Kyrgyzstan and Kazakhstan is a Mandarin variety written in the Cyrillic script.
Wu
These varieties are spoken in Shanghai, most of Zhejiang and the southern parts of Jiangsu and Anhui.  The group comprises hundreds of distinct spoken forms, many of which are not mutually intelligible.  The Suzhou dialect is usually taken as representative, because Shanghainese features several atypical innovations.[26]  Wu varieties are distinguished by their retention of voiced or murmured obstruent initials (stops, affricates and fricatives).[27]
Gan
These varieties are spoken in Jiangxi and neighbouring areas. The Nanchang dialect is taken as representative.  In the past, Gan was viewed as closely related to Hakka because of the way Middle Chinese voiced initials became voiceless aspirated initials as in Hakka, and were hence called by the umbrella term "Hakka–Gan dialects".[28][29]
Xiang
The Xiang varieties are spoken in Hunan and southern Hubei. The New Xiang varieties, represented by the Changsha dialect, have been significantly influenced by Southwest Mandarin, whereas Old Xiang varieties, represented by the Shuangfeng dialect, retain features such as voiced initials.[30]
Min
These varieties originated in the mountainous terrain of Fujian and eastern Guangdong, and form the only branch of Chinese that cannot be directly derived from Middle Chinese.  It is also the most diverse, with many of the varieties used in neighbouring counties—and, in the mountains of western Fujian, even in adjacent villages—being mutually unintelligible.[20]  Early classifications divided Min into Northern and Southern subgroups, but a survey in the early 1960s found that the primary split was between inland and coastal groups.[31][32]  Varieties from the coastal region around Xiamen have spread to Southeast Asia, where they are known as Hokkien (named from a dialectical pronunciation of "Fujian"), and Taiwan, where they are known as Taiwanese.[33]  Other offshoots of Min are found in Hainan and the Leizhou Peninsula, with smaller communities throughout southern China.[32]
Hakka
The Hakka (literally "guest families") are a group of Han Chinese living in the hills of northeastern Guangdong, southwestern Fujian and many other parts of southern China, as well as Taiwan and parts of Southeast Asia such as Singapore, Malaysia and Indonesia. The Meixian dialect is the prestige form.[34]  Most Hakka varieties retain the full complement of nasal endings, -m -n -ŋ and stop endings -p -t -k, though there is a tendency for Middle Chinese velar codas -ŋ and -k to yield dental codas -n and -t after front vowels.[35]
Yue
These varieties are spoken in Guangdong, Guangxi, Hong Kong and Macau, and have been carried by immigrants to Southeast Asia and many other parts of the world. The prestige variety is Cantonese, from the city of Guangzhou (historically called "Canton"), which is also the native language of the majority in Hong Kong and Macau.[36] Taishanese, from the coastal area of Jiangmen southwest of Guangzhou, was historically the most common Yue variety among overseas communities in the West until the late 20th century.[37]  Not all Yue varieties are mutually intelligible.  Most Yue varieties retain the full complement of Middle Chinese word-final consonants (/p/, /t/, /k/, /m/, /n/ and /ŋ/) and have rich inventories of tones.[35]

Question: Which dialect of Chinese has the most speakers?
Answer: Mandarin