Best Answer - Chosen by Voters
I'm a Chinese-American who can speak both Mandarin and Cantonese, in addition to 2 other local Chinese dialects PLUS Vietnamese, so you can trust me on this: I keep telling people that Mandarin is the national dialect. There are more people in the world who are speaking Mandarin than Cantonese. The previous answerer is also right: Cantonese is a local dialect spoken in HongKong, Macau, and Guang Dong province. And, from the early 1900's to presently, it is also the major dialect spoken in the Chinatowns around the world because more businesses were opened by Cantonese-speaking people than Mandarin-speaking people (although this may change because now you have the people from inner China beginning to immigrate and spread out all over the world, and these people only speak Mandarin, and to a lesser extent, their own local dialects). By the way, there are well over 200 different Chinese dialects, and they're all written the same way, but just spoken a little differently. Nowadays, because of the inevitable interactions between the Cantonese and Mandarin people in the world's Chinatowns and Hong Kong, you have people from these 2 groups learning the other's dialect more and more, although the people in GuangDong and HK were pretty much forced to learn more Mandarin (rather than by choice) than before ever since the China takeover of 1997, and China started to open up and blossomed.
But getting back to your question more directly: Yes, it would be better, both professionally and personally, to learn Mandarin over Cantonese. And, although it is NOT easier to learn than Cantonese, I can tell you this much, it is the national language of China, and my personal explanation is that the Mandarins outnumber the Cantonese like 100 to 1. Also, the Cantonese people, like I've said already, need to learn Mandarin, but the Mandarin-speaking people (including the Taiwanese-Chinese) DON'T need to learn Cantonese. I hope all this information helps.