The Ergo is great! Front carry (facing you), back carry, even a side carry that I never figured out how to do, LOL.
Well that's going to always be up to your anatomy and the baby.

I was only ever able to nurse while wearing DS twice. Once at home with the hotsling, but I was shirtless at the time. NOT recommended.
well.....that WOULD solve the too hot problem in Disney! 
And the second time was when he was a year old, during a very long walk in the Moby. And that's it.
One of the things I love about my ring sling is that I can nurse in it so easily, so I guess I'll just have to give it a go and hope for the best.
So for me, the carrier wasn't the problem, but anatomy was.
You ask about the Moby! I felt it was great starting when he was a baby and moving up to some point over a year old. But I had lots of practice in keeping him snug, and re-tying while he was still in it, and so on. The Moby wraps all around you, and is NOT something to wear in a hot climate, IMO. I had a couple swathes of fabric that I tied moby-style, and wore to summer festivals, but I couldn't wear the actual Moby (knit fabric, hot, and adding to that, mine was black) on a sunny day.
A lot have people have said how hot the Moby is and that it wouldn't be a good fit for my 9 month old.
You're talking about facing you while on your front? If so, either one will be great for you. If you're talking about facing away from you, you can't do that with the Ergo (and IMO, as a retired chiropractor, something you should *never* do, even with a mei tai and especially not ever with a Bjorn, b/c there's so little support for the pelvis...with a Bjorn there's no support and you might as well be dangling the kiddo from it's diapered parts, which no one would really do...with a mei tai there's a little bit more support, but not enough AND the baby can't tune out when overwhelmed, the world bombards the baby, nowhere to hide).
Never even thought about him being overwhelmed!
For a couple reasons it took me a LONG time to get to be able to do a back carry (though we didn't even get the Ergo until DS was 2, so I hadn't practiced with that) despite practicing with the wraps, my mei tai, and my MIL's podegi. When we first went out with the mei tai I had to have hubby there to place DS while I tied the straps (that looks funny to bystanders, by the way), and I had to do that for a little while with the Ergo. My joints were blown from the pregnancy, and twisting myself in those ways was at first impossible, and later on just painful, so I was pretty slow in figuring it out.
But once I could do it, oh, it was wonderful! I doubt I would have worn DS on my back at 9 months for hours and hours, but for briefer periods, most definitely. And at WDW you're not going to wear him for hours and hours without changing, b/c you'll be getting on rides and nursing him and such.