The real beauty of the language is revealed in the writing. There are thousands of Chinese characters, but they are not randomly constructed. There is a system to their design, and understanding that system makes it much easier to learn new characters.
There are compelling reasons to learn Chinese Mandarin. Mandarin is the most widely spoken form of Chinese. It is spoken primarily in mainland China, as opposed to Cantonese which is mostly spoken in Hong Kong, Southern China and across the Chinese diaspora. But even in these locations, Mandarin is generally understood and it shares a common writing system with Cantonese. In addition to this, Mandarin only has four tones, making it easier to learn for Westerners than Cantonese. If you plan to use Chinese to communicate with people from mainland China, then learning Chinese Mandarin is probably the best option.