As you can see, there are many diverse factors that must be taken into consideration before emending a text. A critical edition of the text must take into account all of these factors before suggesting a preferred reading. This is not the place to go into detail on the history of critcial editions. (The first was Meir Ish Shalom's Maakos and a bit later H. Malter's Taanis - there are various uselful aids starting from Dikdukei Soferim until Dikdukei Soferim HaShalom. S. Y. Friedman's school is doing some great work but unfortunately much of it is not easily accessible to the general public and the multitude of manuscripts cited is confusing to the lay-reader.)
I wonder where the Oz V' Hadar gemaros stand on all this. The editors freely admit that they in no way intended to produce a critical edition. Thus in their hagahot we have "Kesav Yad", "Defus Rishon", Rashash (,etc.) and then a whole host of some modern-day scholars (Devash Tamar, Be'er Mayim?) whose work I am not familiar with. The hagahot are incomplete as many inportant hagahos that are necessary to understand the text (even from a common source like Dikdukei Soferim) are missing.
Have any reviews been written of this edition by a professional scholar? How did the authors make use of earlier critical editions written by "Maskilim" like Malter and Ish-Shalom? Did they make use of the scholarly editions? (If not, shouldn't an attempt be made (at least for future editions) to prepare a popular Shas that makes us of the work of these scholars?)