Thoughts:
Exam: anywhere suitable, and make the numbers work.
Real world cross-country in GA - I'm far more likely to divert due to weather or serviceability than I am due to a problem at my destination. So, I actually will have a series planned along my route - which really only means making sure I have visual and instrument approach plates readily to hand for my selection of choices. The diversion itself I just fly like an exam exercise - just route from a convenient waypoint along my existing route.
And just like the emergency exit, always remember that the best alternate may well be behind you!
Real world jet operations - pick the nearest legally feasible alternate to the destination, that way your landing fuel can be minimised, and so payload maximised and costs minimised.
G