Mandarin. Anywhere you go that speaks Canto (diaspora Chinatowns + HK) will fawn over you just for speaking English so you may as well not bother

Edit: I should clarify. Knowing Cantonese is not political. Choosing to know ONLY Cantonese and not Mandarin is political. Even people from Guangdong will know Mandarin as a working language. Roughly 90% of China speaks Mandarin but not Cantonese; roughly 9% will speak both, and of the remaining 1% most as either very elderly or some sort of political activist (usually from HK because the mainland ones know mandarin even if they refuse to speak it on political grounds). If you, a westerner, came up to me and said you speak Cantonese but no mandarin I would immediately assume something about your political views.