Cruelty: the ground most cases run on
Cruelty is conduct of such a character that the petitioner cannot reasonably be expected to live with the respondent. It covers physical violence, but the great majority of pleaded cases concern mental cruelty: sustained humiliation, false allegations, desertion of responsibility, financial deprivation, or persistent conduct that makes the marriage unendurable.
What courts want is specificity. A petition asserting that a spouse was "cruel and harassing" achieves very little. A petition setting out dated incidents, with corroboration where it exists (messages, medical records, complaints made at the time, witnesses) is a different proposition entirely.
The other statutory grounds
Each has distinct ingredients, and pleading the wrong one is a common and costly error.
Irretrievable breakdown: the ground that is not one
Despite widespread belief, irretrievable breakdown of marriage is not a ground under the Hindu Marriage Act. Law Commission reports have recommended adding it; Parliament has not done so.
The Supreme Court has, however, dissolved marriages on that basis in the exercise of its own powers under Article 142, where the marriage was beyond repair and the parties had been separated for many years. That is a remedy available from the Supreme Court, not something a Family Court can grant: which is why, in practice, long-separated couples are better served by converting to a consent petition than by waiting for a breakdown ground.