Choose a post whose usable scratching surface lets your Maine Coon reach upwards without running out of material. There is no single height that suits every member of the breed: a long adult and a growing kitten can have very different reaches. Watch your cat stretch against a surface they already use, then compare that reach with the scratching section in the product measurements. Overall product height can be misleading when a decorative topper, cushion or bare connector occupies part of the post. Ask for the height of the actual scratching material if it is unclear. Also check that your cat can stand comfortably at the base rather than on a narrow rim. A suitable height is only useful when the assembled post stays steady under normal use and fits its intended position.
For example, a 90 cm product with a 20 cm decorative top may offer only 70 cm of scratching surface. Compare that usable section with your cat's observed reach; the headline height alone would hide the difference.
For product comparisons alongside this advice, see Sisal Pair scratching mats and Paw-Villian cardboard scratcher. The details below explain their sizes and uses.
Further reading: cats.org.uk.
Sisal Pair scratching mats
Paw-Villian cardboard scratcher
Scratch Central