At the STM we alway recommend the heaviest weight cloth that is available within your budget. It's a good formula.

First decide what tartan you want, in what color scheme, as this obviously has the most impact on how your kilt looks.

Then, from there, see what weight ranges are available (remembering we can always have the heavy weight custom woven). That may or may not limit your choices.

Finally, from those options, go with the heaviest weight within your budget. We describe the difference between light, medium, and heavy weight as, "good, better, best." We would not sell you a poor quality kilt, but we want you to get the best you can, because in the long run we know folks will generally be happier in the heavy weight kilt.

Like Rathdown, when some is specifically looking for a cooler wearing kilt, we recommend one with less yardage, as this will have more actual impact on the temperature, without sacrificing the benefits of the heavy weight wool.