If you live in Burlington you probably know that there aren't all that many flights out of Burlington, but AA has a decent number of them, maybe even more than United. AA will fly you to one of their hubs: Philadelphia, Washington DC, or there is one flight to Charlotte. Once you get to any of those hubs there are lots of flights to MCO, so if you miss your connection there is a decent chance they can find you another one. Obviously going back to BTV is more of a luck of the draw kind of thing.
I've flown in and out of Burlington, all on AA, a lot. Always made it to my destination the same day. My daughter went to school there, and flew United a lot. Her United flights gave me a lot of grey hair, and she spent a few nights in airports trying to get into or out of BTV. Weather in BTV is seldom an issue, but BTV is not a popular destination, so flights in and out of there get cancelled, and from our experience United seemed more prone to do that than AA.