A few renderings of a well-known title, some common, some probably confined in appearance to this post:
Mahāparinibbānasutta
Mahā Parinibbānasutta
Mahā Parinibbāna Sutta
Mahā Pari-Nibbāna Sutta
Mahā-parinibbāna-sutta
Mahā-pari-nibbāna-sutta
Which is best? This is essentially entirely an issue of subjective taste, as Pāli literature is often devoid of longer Indic titles such as the Āryaniṣṭhāgatabhagavajjñānavaipulyasūtra or the
Āryasarvabuddhaviṣayāvatārajñānālokālaṃkāranāmamahāyānasūtra!