ICU: Which compare API to use?

I read the documentation on the different compare APIs that ICU provides, but couldn't quite get the difference between them.

int8_t icu::UnicodeString::compare  (const UnicodeString &text  )   const

int8_t icu::UnicodeString::caseCompare  (
        int32_t start, 
        int32_t     length, 
        const UChar * srcChars, 
        int32_t     srcStart, 
        int32_t     srcLength, 
        uint32_t    options 
    )       

virtual EComparisonResult icu::Collator::compare(   
       const UnicodeString &source, 
        const UnicodeString &target 
    )   

To be able to do case insensitive operations on UTF16 strings, which API fits the bill and why?

Thanks!

Copyright License：
Author:「Maddy」,Reproduced under the CC 4.0 BY-SA copyright license with link to original source & disclaimer.
Link to：https://stackoverflow.com/questions/36620022/icu-which-compare-api-to-use