Assuming both speakers have the same size and type of box, the lower efficiency speaker will have deeper bass. High efficiency and deep bass at the same time requires a large box (or a creative marketing department!).
Now if box size isn't an issue, the advantage offered by the high efficiency speaker is typically better dynamic contrast and a greater sense of liveliness. High quality high efficiency speakers often sound better at low volume levels and often have a more tube-friendly impedance curve (apart from needing less power, which in and of itself is a tube-friendly characteristic) - but there are exceptions.
There are other generalizations that could be made, but on the other hand there are exceptions to just about every rule (except for the tradeoff relationship between bass extension, box size and efficiency).
Duke
Now if box size isn't an issue, the advantage offered by the high efficiency speaker is typically better dynamic contrast and a greater sense of liveliness. High quality high efficiency speakers often sound better at low volume levels and often have a more tube-friendly impedance curve (apart from needing less power, which in and of itself is a tube-friendly characteristic) - but there are exceptions.
There are other generalizations that could be made, but on the other hand there are exceptions to just about every rule (except for the tradeoff relationship between bass extension, box size and efficiency).
Duke