Probably what Bioware intended. That means American for tougher races and British for weaker ones. Specifically, Qunari and dwarf get American and human and elf gets British. Bioware has said that those are the default voices for the respective races, and I see no reason to deviate from that. After all, the American voices in DAI sound a little too tough to fit a human or elf, and the Brit voice sounds way too soft and posh for a Qunari or dwarf.
I disagree really. All voices can be made to work with all races.
The American voice can work for all four races, especially since Qunari, Elves, and Dwarves have spoken American before and Humans can speak American... on Earth 
We don't know what accent Ostwick humans speak so they don't necessarily follow the Fereldan style. Kirkwallers spoke like Fereldan but Starkhaven was Scottish. Ostwick can be anything.
The British voice only appears to "fit" for Humans and Elves because Elves speak a Britannian accent in DA2 and Humans in Fereldan have always spoken British.
Qunari and Dwarves may sound weird, but the former being Vashosh and the latter being a Surfacer, they could have developed any accent depending on their place of origin. Granted it might sound out of place if you meet your family and they all speak the default American.
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Personally, I'm going to always stick to the defaults because it's what I'm most comfortable doing. Although, I might switch up and have Humans use American once in a while.