Hi, I am from Oil & Gas sector and plan to do an MBA (online) from a reputed university to transit my career into business consultancy companies.

I have a few schools in mind, like Manchester, Aston, Robert Gordon but unable to decide which specialisation and school I should choose.

Appreciate the responses.

Focus on schools, not specialisations. Which schools do your target firms hire MBAs from in your target geography? If you research their websites, or in LinkedIn,  you will find the most effective path.