Who should the US top 5 allies be

[Crumpets]

The US is in kind of a weird position in that we can't really expect much from our allies in exchange for all we give them. The best we can hope for is that, by giving them economic, political, and military support, they can ensure stability in their immediate vicinity. Looking at what regions are of the greatest strategic interest to the US, I think it would probably have to be North America (obviously), Western Europe, and the Pacific Rim. So something like this overall:

Canada
Mexico
The EU (especially Germany)
Japan
Australia

Post-9/11 I would have probably switched out Japan and Australia for Israel and some modestly democratic Islamic country such as Turkey, but I feel like in the past few years, the strategic value of the Middle East has diminished significantly for the US.

It'll be interesting to see how the US deals with a post-Brexit UK. Obviously the two countries have so much in common and rely on each other so much economically and culturally that we're essentially tied together for the foreseeable future. At the same time, in a purely realist sense, the relative standing of the UK as a strategic partner diminishes significantly as a lone actor, relative to when it could hold a greater sway on the rest of the EU and their respective militaries.