The first option, manually deep copying your values, will be the most performant by far.
Reflection will introduce quite a bit of overhead, as it is (relatively) slow to access data.
Serialization is adding a huge cost, as it serializes the data into a temporary structure, then reverses the process to set. This is again, very slow.
The only advantage to option 2 or 3 is that its potentially easier to implement, and reusable across multiple types. The first option has to be hand-written per type, but is much faster (and more efficient in memory usage than option 3, as well).
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