i made a thread about this in the chillout room, so ill copy and paste my feelings about the channel trailer, i feel it has its ups and downs......
"having actual trailer:
pros - since it only plays for unsubscribed people, you can tell them to subscribe, and let them know all the content on your channel, and give linked annotations to certain playlists and stuff.
cons - might ignore it since its not an actual video and might just click out in laziness to click around to see content.
using a normal video:
pros - can use your best video and grab their attention fast.
cons - they might not like that specific video, and instead of clicking around to other vids, they might just leave."
having said that i feel it also depends on your content.... if you do the same content every video, a trailer is useless because they will see what you do from a normal video of yours, but a channel like mine for instance, we do pranks, challenges and vlogs, 3 completelt different types of videos, so if we have a challenge as our main video, that might not be there thing and leave, but they might love pranks, but not even look around due to the main video being a challenge ya know? were thinking about making a trailer, where we get it out there quick that we do pranks, challenges, and vlogs, and give them an easy way of navigating through out diff vids with annotation.
sorry for the long response, but i feel this is the best response to this question lol