SO what made these two lamp shapes come to be? it seems if one had some sort of advantage over the other it would have over taken the other type... what are the advantages and disadvantages of each lamp shape??

Add in U tubes and PL's for the more complete image

The U tubes and circlines were the early attempt to shape Fluorescents towards specific application, in their first years. The U tubes for example were intended for troffers to make a uniformly lit area, without using double the quantity in linear lamps (and respectively higher losses)

The 2Ds and PL's are much later developments, based on better technologies (Triphosphors, narrower tube diameters), with more accurate and complex shaping, and intended for better optimized luminaires. They were intended for about the same applications, with the 2D being pushed in the UK by Thorn, and PL pushed in Europe continent by Philips (and adopted also by Osram)

The overall result seems (to me) that 2D/PL are better than circlines on most accounts. So i'd prefer either of them over a circline

One thing I do like about Circlines is that they do come in Halophosphate colours as well as Tri.
My favourite lamp has to be the 2D though.