Hi Desiree, As a Chinese native speaker, I suggest you learn Chinese Mandarin first. Because Cantonese is a dialects in China and it is not a common language in China. Cantonese is used in the south of China, most of people in the north of China do not understand Cantonese. If you learn Cantonese, you will have language barrier in China. So it is the best choice for you to learn Chinese Mandarin. Because everyone in China can speak and understand Mandarin no matter where they live. Good luck!

It depends on where you are going....Cantonese is a local language used in GuangDong, Hong Kong & Macau. In general, it is better to learn Mandarin first as I guess 99% of Chinese understand Mandarin. Learning Mandarin is also easier as there are lots of learning material for self-study. Mandarin & Cantonese share nearly the same vocabulary set, but the pronunciation is "completely" different.