I say, with Allah's success: If the sky is clear: it is preferable to delay Isha until the first third of the night; as narrated by Abu Barza, may Allah be pleased with him: ((The Messenger of Allah, peace be upon him, used to delay Isha until a third of the night, and disliked sleeping before it)), in Sahih Muslim 1: 447. And from Abu Huraira, may Allah be pleased with him, the Prophet, peace be upon him, said: ((If it were not a burden on my nation, I would have delayed Isha until a third or half of the night)), in Sahih Ibn Hibban 4: 406, and Sunan al-Tirmidhi 1: 35, and it is authenticated. However, if the sky is cloudy: it is preferable to hasten Isha; because delaying it reduces the congregation considering the rain. See: Al-Wiqaya p.137, and Al-Kanz 1: 83, and Allah knows best.