I own three buffs and five shemaghs.
Interestingly I only bought three of the shemaghs, last year they kept popping up on sunday mornings around the city, Guess people lost them drunk and didn't care So I claimed them for myself. Yellow ones washed with green ones soon becomes green...
My new cheap black one is the one I wear most now. just thrown it over the shoulder under my jacket or shirt.
I used to wear my buff constantly, now I have an akubra again so the buff is actually wrapped under my hat band. It still comes in handy.
I have used the shemagh for everything for wrapping me up to wrapping up the shopping, furoshiki purse style thrown over the back.
I have never managed a comfortable fundoshi with it though...too warm...
But a shemagh around each leg as chaps under trousers is a great base layer for trapping heat in winter as long as it's tied up properly so it won't fall down.
I have a list as long as your arm for using shemaghs, buffs, bandanas and woolen blankets.
But if I were to choose only one for regular wear it would be the shemagh, it's size really does matter.
I am thinking any scarf around 105cm x 105cm in an absorbant material that dries fast would be a welcome addition to any kit list, however the 3000 yr old woven design used in the shemagh...Well it has it's own ancient history, more than can be said for most kit.
Although the buff too, was a modern reinvention from a victorian snood...a peasants hair tye.
I haven't picked up a merino buff yet, but will be getting two of them, like john I have an unnatural bond with the stuff, And he will probably agree, when you wear nothing but merino as a base layer for long periods your body adapts it's self some how. I have 6-7 merino base layers now, I still want more...
I am rambling on here but what it comes down to
Get s shemagh first, then get a buff, then if you don't have one, get a woolen blanket.