People in different parts of China may have different accents. But they will speak Mandarian to make you understand. So don't worry.

if you want to learn mandarin, you'd better go to north china. because in south china people's mother tone is not mandarin

Chinese has many different accent in different areas. In Bejing and Harbin, we pronounce without too much accent, maybe you could practice mandarian better. However, for poplulation transfer, mandarin is almost the same all over china, and many people could speak it very well in different cities. So don't worry too much about your location