well, i currently live in sierra leone and i can honestly say it's a pretty terrible place to train. torrential rains, brutal heat, not much food . . . i manage to run, and do some dryland, and that's it. i surf and swim a bit when i go to the coast, but that's not often enough.
previously i lived in kenya, in the high rift valley. as running goes, it might be the best place on earth - altitude, good roads, trails and tracks, better food options, and the company of literally the best runners on the planet. on the other hand, almost no swimming, and cycling is basically suicidal.
my permanent home base is zurich, switzerland, and for me it's the best i've ever had. a 25m indoor pool about a 4-minute walk from my house, a 400m mondo track about a 5-minute run from my house, and the best road cycling of my life at my door. i've got hills, flats, rollers, trails . . . you name it. courteous drivers, good competition, and all the races and resources you could need. downside is cost, no doubt.
on that front the 'best' might be the place where you've got a free couch to crash on or something. it also has to be said that 'best' is relative: i lived for 2 years in edmonton. no OWS options, limited road riding in the city, and a long and incredibly cold winter. but i was in the best shape of my life there, because i hung out with really fast people, commuted by bike, skied nordic all winter, and had a lot of time to train.
so . . . it depends.
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https://lshtm.academia.edu/MikeCallaghan http://howtobeswiss.blogspot.ch/