My personal opinion is forget the boarded ones and get a good pair of lycra ones. I have worked my way through a number of shaped ones, and some are better than others, but all left me with the feeling of why bother.
And I have the same experience regardling length - even sometimes within the same brand. My answer has been trial and error in finding types - brand and style which fit - and even then I have gone sadly wrong. The all time low has been one pair which I wear as socks, with elastics, under floor length casual skirts.
cariad