I have had extensive experience with each.
The differences are not subtle. I love Bill Conrad, and have a good relationship of mutual respect with Lew Johnson. Through the years I have sold tonnage of their gear. However, the Avatar, which costs more is more to my liking. It is cleaner, clearer, soundstages better, and has fewer of the tube colorations, some of which I find negative. The Avatar played the dickens out of the Vienna Acoustic Mahlers. Deep rich soundstage, great bass, and honest to God, the most stable and easy to use bias I have ever seen. All in all a great product from one of the industry's truly good guys, Kevin Hayes. If you do decide to get one, you will love it. There is now a Super Avatar with 80wpc, which I have not heard, except vicariously through Kevin. Good Luck and Good Listening.
Larry R. Staples