I didn't even know about AWS SSL, LetsEncrypt works out of the box, IMO it's a very easy setup for most scenarios. AWS SSL sounds like it will only work on AWS.
Yeah! But, the best part here is that we're getting AWS SSL, out-of-the-box; id est, no beta-list, no domain-preverification and all of that. IMO, AWS SSL sounds better. Honestly, I wasn't able to try LetsEncrypt because of that "domain waiting list". :(