Prefer who or that over if, if you can:
The difference may seem slight, but if adds a conditional clause which is best separated from the rest of the sentence by a comma. The construction with who does not need this: it is experienced more readily as a single sentence. This is easier to read and process. This consideration applies if you have only 1 condition, or few conditions.
if is often useful, for example if you have a long list of conditions:
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