Everybody I can think of uses cometic gaskets, & everybody on this site has said good things about them. I believe that's the general consensus amongst the QRHQ builders also. I personally have never toore an engine apart so I can't tell you from personal experience. I'm sure iceracer could chime in and answer your question since he rebuilds them.
I have had good results with all of the Cometic gaskets except the head gaskets. I have not found ANY head gaskets for the LTs other than OEM that are consistently good.
And It looks like OEMS are made by Cometic now or the same material. As much as I dislike screwkng with copper head gaskets of an had to run one that's what it would be. Glad I do orings.