Mylites is just the branding for the mylar bags that are made by E. Gerber. They come in both 2 mil (Mylites2) and 4 mil (Mylites4) varieties. Both are made with Mylar D.
As mentioned, 2 mil mylar bags are sufficient for most people.
I have not tried the mylar bags made by BCW, but I tried the ones made by ComicProLine. The ComicProLine mylars work, but they are definitely a step down from the mylars made by E. Gerber. My ComicProLine mylars often have rough edges and don't have the same solid feel as the E. Gerbers.