Which conformation is the most stable for cyclohexane, is it the boat conformation or the chair conformation?
The chair conformation is clearly the most stable conformation.
The chair conformation clearly minimizes the number of transannular interactions. Given the chair form, each face of the ring has 3 axial substituents that sterically interact, versus superposition of 2 hydrogens at each end of the boat.
When the ring is substituted with a butyl group or even a methyl group, the conformational preference for equatorial substitution is even more marked.
How do you rationalize this? Make a model, and consider the transannular interactions yourself.