The Taiwanese, The PRC and The Singaporean

Ben and I have quite a number of foreign friends and this is what we've observed:

The Taiwanese always say

搞不好，eg: “ 搞不好他明天不来了.”

The PRC will say

说不定，eg: “ 说不定他隔天儿不来了.”

And The Singaporean usually say

“ Sekali tomorrow he won't come aH ! ”