Which is Better/Faster isEmpty() or isBlank()?

String.isEmpty is marginally faster (~0.00219ms vs ~0.00206ms, about 6%). This is such a trivially small amount that there's no reason to worry about which one you use from a performance perspective.

Practically speaking, you should generally use String.isBlank if you expect potentially whitespace strings (e.g. from user input that may be all whitespace), and String.isEmpty when checking fields from the database, which will never contain a string of just whitespace.

Faster here is very broad to classify, as you will need lot of considerations to test that out. It depends on what is your use case and accordingly which method fits in best.

String.isBlank handles any string even with white space, whereas the same is not true for String.isEmpty. So if you expect empty string ('') always, then using either of them should be fine.