SWK offers Acrylic or Wool kilts
USAKilts offers PolyViscose or Wool kilts
Burnett's and Struth offers Wool Kilts

In my opinion the best fabric choice for a tartan kilt (unless you live in the tropics) is wool.

Second best choice is PolyViscose.

In my opinion Acrylic comes in third - with issues of sagging, bagging, and pilling.

I heartily agree with those who say buy the best kilt you can afford - unless its likely to get damaged where worn. SWK, USAKilts, B&S all make fine kilts but you will find differences in fit and finish based on the price point of the kilt.

Good luck with your decision and have fun in your kilt!