A common thing to do to utility classes is to give them a private constructor:
public final class UtilClass { private UtilClass() {} ... } >
public final class UtilClass { private UtilClass() {} ... }
Using enum for something that's not actually an enum is ugly and confusing. I'd say that's enough reason not to do it.
enum
The "utility class" pattern is perfectly legitimate. If your tools don't like it, that's a problem with the tools.