I have Tiagra shifters in one bike (my old road bike) and Ultegra in the other. The 105 shifters have the same shape as the Ultegra, as far I can tell. I hate the Tiagra ones. I have small hands, but my palm does not get support on the Tiagra shifters. The shape is odd and uncomfortable.

I found web page with pictures of both shifters side by side for comparison:
http://geodee.com/2010/05/a-non-gear...t-impressions/