There are a few things that you will need to consider:
As Unclegus has said, you are arriving at the start of a 3 day national holiday in Scotland, where much will be closed.
Sunset is c 3.45 pm at that time of year.
Who knows with the weather - it maybe OK or it could be quite cold or snowy.
Accommodation availability may be reduced, as most people booked months ago. Some, more rural places close over this time of year.
Locals travelling over Christmas and New Year booked their flights months ago, as soon as the best fares became available.
What do you want to do when in Scotland? It's pointless us recommending an airport if it doesn't fit with what you want to do. There are hundreds of must see attractions in Scotland, so some guidance from you would assist in providing something useful.
Flying back to the US will be easier from Scotland rather than backtracking to Ireland. Try Skyscanner for route options to your home airport. This also impacts on whether to hire a car - it isn't needed in the city centres. There maybe engineering work taking place on rail routes, which may delay services.