Rewards are random. If we discuss a specific Level for example, Green Dragons which are level 79, and Steel Dragon level 249. Now these both drop level 3 Treasure Trails, but the Steel Dragon could obtain you a reward not as good as a Green Dragon could, or the other way around. So if you are speaking about a particular Treasure Trail, the Monsters that drops that particular level, will not judge what reward you will get. Each level has it's own 'Best Items', but within each level, rewards are random.