Q:

How legitimate is the phrase "from which one to choose"?

Here's an example.

If you want to get a PC and you don’t know from which one to choose, choose something simple.

It doesn't look consistent logically, but another person insists this is the correct form. I find it irregular because it's not exactly a choice if there is only one of... well, anything to choose from.
Is that phrase really better than either of the following examples?

If you want to get a PC and you don’t know which one to choose, choose something simple.

or

If you want to get a PC and you don’t know from which to choose, choose something simple.

A:

"from which one to choose" isn't idiomatic English and doesn't make sense: you can't choose from one.  
You have to choose (or select, or pick) from a collection, or a set--from more than one, in other words.
choose from those offered in the store
choose something simple (from those offered or from those available)

