Which is more efficient, "data.Length==0" or "data==string.Empty"?

Question

I want to check whether or not a variable string data contain empty string.

Which is more efficient, data.Length==0 or data==string.Empty?

I forgot to say, the data has been checked and it is guaranteed to be not null.

Answer 1

Test results for 100 million iterations:

Equality operator ==:   796 ms 
string.Equals:          811 ms 
string.IsNullOrEmpty:   312 ms 
Length:                 140 ms  [fastest]
Instance Equals:       1077 ms 

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