I have the Shebeest knickers and the LouisGarneau Ergo Sensor knickers. They are both REALLY nice. Both have nice chamois and are well made. Yes, the Ergo has good weight fabric. Shebeest is a bit snugger in fit than the Ergo. Love the Shebeest too, though, and neither knicker has "diaper butt" effect.
I love the blue line on the Ergo- very sleek.
I have them both in Medium- I'm 140 lbs 5'5", pearshaped. Both fit comfortably snugly, as I prefer. If I were 10 lbs heavier I'd probably want to get the Shebeest in a large. I could probably still fit in the medium Ergo though.