I guess, unfortunately for us, we're still looking into K-1, about to send the petition in fact. Hopefully something changes in those 15+ months we'll have to wait. Don't you only have 4 months to get an interview after i-129f gets approved? If so, then going through the whole Shengen route sounds risky still.
Why would you advise the marriage visa? Isn't it the same story as fiance? As far as I understand, it takes even longer on average...