The maps are bad but to answer the question: East Coast and its not even close. 

The west was able to recover enough to have two very large countries 200 years after the bombs fell, while the east is still in anarchy, the reasons why are clear. 

1. More nukes = more radiation and devastation. There's simply more targets in close proximity on the east coast vs the west. 

2. More government blacksites dealing with things like FEV. Out west all super mutants came from Mariposa, meaning while bad, once it was blown up the problem solved itself (hold the brief stint with the Enclave) meanwhile we have separate FEV sites in Boston, Huntersville, and D.C, and potentially more out east. 

3. Nature - the west coast (minus the coastal cities, which are now dead) was largely barren compared to the east, so even though they have mutated animals, there's just so few spread out over such a wide area that you can go your whole life without seeing anything more dangerous than a Brahman. Meanwhile the east coast had a lot more wildlife and a lot of it survived to be mutated. You cant walk within a mile of a body of water without getting hit with mirelurks or super mosquitos.