For the new raid, I too believe Thunderlord will be the gun to have. He's never sold it, but supposedly he's be selling it the week before HoW launches. Gjallarhorn may never be sold again. Not saying it can't be, but you have a couple more weeks before we have some new exotics entering his loot table, and we know BungieVision will push that DLC by restricting Xur for a few weeks.