I have used a Snugli, Nojo Babysling, Maya Wrap, New Native pouch, didymos wrap, a Kelty backpack and a Baby Trekker (very similar to the Ergo, which I think is nicer looking, but not available back when I got my Trekker).
For travel (and particularly WDW) I don't recommend the large frame backpack like the Kelty or a padded ring sling like the Nojo. A Snugli would be fine for a small baby, but hard on your back and shoulders for a larger child. Same with the Bjorn. I think I"ve seen the hip hammock and I have to say that thing looks like it would become uncomfortable very quickly. For a hip carry I'd recommend the Maya Wrap, or for something even more compact, the New Native. Both can be adjusted to wear comfortably for long periods of time (the secret is to spread the fabric wide over the supporting shoulder...do not let it come up to your neck and the further down the arm you can get it the better) The Trekker has a lot of padding and could get very hot at WDW in the summer...in cooler months its great. It can be worn on the front or the back. If you have plenty of time to practice look into a didymos or ellaroo wrap....if you can get the back carry to work for you I think this carrier is ideal. That said...I've never been able to manage it myself. Wrap style carriers are definitely the most comfortable, particularly for those with back trouble (ie. ME!). You can also use one of these carriers for a hip carry, but will tend to have lots of extra fabric.
If your trip is in summer you can get a sling made of Solarveil fabric...light and airy, yet sun protective. Once again I stress that the best item for a hip carry is a sling. It frees up your arms and doesn't put too much stress on the neck back and shoulders.
Check ebay...that's where I sold my Kelty and bought my Trekker. You can probably find some good deals on good carriers.
NurseKim...love your sig! That's my superpower too!