Definitely depends on what you're hunting - and greater dragons can actually be a terrible choice in some situations. Take Corgul, for example. GD's do 100% physical damage, and Corgul's physical resist is extremely high. Corgul does high damage percentage in poison, and poison is the GD's weakest resist. So GD's are not a good choice at all for Corgul. (Rune beetles are a good choice vs. Corgul, as they do high energy damage, which is Corgul's weakest resist).