に限る|にかぎる

1. 1Nothing beats X; X is the best thing to do or have (speaker's subjective opinion).Ex. 1
2. 2Limited to X only, as used in rules, notices, and conditions.

Sense (1) is common in everyday conversation for stating what you personally consider best, often with a topic like 〜時は or 夏は and a softening particle such as ね. Sense (2) appears in formal notices and regulations. Unlike ほうがいい, which gives advice, or べき, which states obligation, sense (1) expresses a personal conviction.

• に越したことはないN2「に越したことはない」 overlaps with 「に限る」 only in the 'best' sense: it states a generally accepted truth in an objective, tactful tone and often implies it is fine if you can't manage it, while 「に限る」 is an emphatic judgment based on personal experience. 「に越したことはない」 has no 'limited to' meaning.
• に限ってN2「に限って」 cannot end a sentence as the predicate and must be followed by one; it means 'just when (something unwelcome happens), of all times', 'that one person alone, unlike others, would never…', or simple limitation, and never 'best'. Its limiting sense is close to that of 「に限る」, but 「に限る」 is used at the end of the sentence, whereas 「に限って」 sits mid-sentence and modifies the following predicate.
• に限らずN2「に限らず」 is the negation of the 'limited to' sense of 「に限る」, meaning 'not limited to…'; it follows a noun, appears mid-sentence, and is often paired with 「も」 in the following clause. It has nothing to do with the 'best' sense, and the two are not interchangeable.
• ほうがいいN5「ほうがいい」 mainly gives advice to the listener, though it can also express a preference in comparisons, and when advising someone to do something it usually takes the た形. 「に限る」 in the 'best' sense is the speaker's experience-based assertion, does not use the た形 after verbs, and is ill-suited to advising others.
• べきN3「べき」 expresses 'should' grounded in reason, common sense, or obligation, typically in assertions and advice, whereas the 'best' of 「に限る」 comes from personal experience and feeling, voices a preference, and is not suited to advising others. The two are generally not interchangeable.

に限る asserts X is simply the best, whereas に越したことはない means X would be preferable but is not essential, ほうがいい gives advice, and べき states what one ought to do. に限って means 'precisely when/of all people' (usually with an unfortunate outcome), and に限らず means 'not only X,' so neither shares the 'best' meaning.