Past simple would be "I chose X". I agree that it would sound reasonable to say that. If you want to tell somebody that you are now choosing X, then saying "I choose X" makes sense. If for some strange reason you need to express the idea that you chose something in the past and that choice affects the present, then using "I've chosen X" would ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.