Question

Which conformation is favoured?

Answer 1

The isopropyl substituent is much bulkier compared to the N-propyl substituent, and is also less flexible. As a result, having the isopropyl group in an axial position would create more steric strain with axial hydrogen atoms. If the N-propyl group were axial (as shown by the right figure), it would have some ability to bend away from the other axial atoms and help lower steric strain. I would say the right figure is the favoured conformation.