In stead of asking “would you reccomend”, shouldn’t you rely on “how did you learn about us?”, or “why did you buy our product”, the first one being the most reliable, as it is a neutral question about a fact.
Asking "How did you learn about us?" is a question that helps evaluate your marketing and sales pipeline. Asking "Would you recommend?" is about helping your product development process. Your sales / marketing team can't effectively influence the NPS (only thing they could do is divert marketing from customers that wouldn't be satisfied by the product).
I still think that it is useful to track actual reccomendations when that is expected to happen.
I agree that it's very useful to track where your leads come from, and I love the short radio button lists that allow you to select a source.
If you feel like you should only ask one question, and it's either that or the NPS question, then it really depends on what your goals are at that point. Are you trying to figure out if your customers are happy with your product, or are you trying to figure out which of your marketing channels is most effective?
I think tracking NPS over time is really powerful, so then you're tracking not an absolute number, but you're tracking if customers have recently changed their opinion of you.