difference - Each vs. Either

I wrote:

For example, in English where phrases of a sentence have an almost fixed order, using the phrase structure is more common, while for languages with more flexible word order, the dependency structure is more suitable. This choice also depends on the power of the available parsers for each formalism.

for each formalism or for either formalism? what is the difference?

I think if I use each, I mean they consider the power of the parsers for phrase structure and the power of the parsers for the dependency structure and then decide based on the comparison

but I don't know the effect of either, and what would be the meaning if I use either.

Answer

Each indicates a definite property. There is no way around it: the choice will always depend on the power of available parsers.

Either indicates a tentative property. Perhaps the choice depends on the power of available parsers for some formalisms, but other formalisms can be chosen regardless of the power of available parsers.

Admittedly, for the example you gave, the difference is not that great, and each and either can be used almost interchangeably.

Perhaps some better examples:

Each party may lose support given the recent crisis

In this case, any party in our fictional country may see angry voters.

Either party may lose support given the recent crisis

Some parties may lose support, because they handled the situation badly. Other parties may not see an effect, perhaps because their voters don't care about the crisis at hand.