I would choose iso(butane) over n for a variety of reasons..
"........ hydrocarbons with straight chain molecular structures,.. these types of reaction steps are a major part of the mechanism.. for those with branched structures there are more attractive alternatives that suppress the last step shown(which was ..reactive free radicals build up leading to self sustaining reaction) for example, a rearrangement reaction to an alcohol plus a ketone.
It is ironic... branched chain molecular structures proceed via simple radical chain mechanisms, while straight chain molecular structures react via branched chain combustion mechanisms, which can get quite explosive and unstable.
autoignition thus occurs at a quite low temperature for a hydrocarbon with a straight chain molecular structure, but a much higher temperature will be needed to produce a self-sustaining reaction in its isomer with a branched chain molecular structure...... The autoignition temp of n-butane(straight chain) is 288 degree Celcius while that of isobutane(branched chain) is 460 degree Celcius................ . The intermolecular interactions of isobutane are weaker than those of n-butane because it's a compact molecule and doesn't stack as neatly with itself. This makes it more volatile..easier to purge, a boiling point about 20 degrees lower and gives it a higher vapor pressure....remember that imfs are what create polarity as well and is why hexane is superior, to butane ...iso butane is less polar than n butane and will produce a cleaner extraction......its quite literally better in every way "