I have used both and I have also used the Sigma product Metro. I found no discernable difference in quality of thread. I do try to support made in the USA business and products whenever possible. so my only beef with Sigma and Metro is that both products are made in China. Glide is USA made.
Both Sigma and Metro are very shiney threads. Even more so than glide. They don't seem to sink down into the fabric as much as the glide. Glide is a 40 wt but it really has a look and feel of a 60 when quilting with it.
If you do a lot of charity quilts and don't have the "political" stance I do of trying to support made in the USA whenever possible, even if it means paying more, (Which I will do if I am getting a quality product AND helping to keep an American employed in the manufacturing sector), by all means go with the Sigma and Metro.
Also, I have only recently tried these products so I can make no claim to their durability in a quilt. But they look pretty and run through the LA just fine.