I have prepared an XLS file comparing the four different databases for Chinese Republican (and late Qing) periodicals currently on the market, i.e. Shanghai tushuguan's 晚清期刊数据库 (I do not have a list of the journals contained in their 1000 title Republican sequel yet, but I work on it :-)), Apabi's 民国期刊, Dacheng's 大成老旧刊全文数据库 and Hytong's 瀚堂近代报刊. I start this as a new thread here under an "open" category, to allow outsiders to CrossAsia to share our discussion. This is also why I do this in English (you may use whatever language you prefer :-).
Not to forget: Some time ago we have already started to discuss Republican journals DBs resp. the Dacheng database in an "internal" category (please see the very helpful commentaries of "Xiuwen" from the 2nd and 11th of March 2011: LINK.)
I now have compiled an XLS file to share it with you, which compares which and how many journal titles contained in one of the named databases do also appear in each of the other databases. I did this by comparing up to the first four characters of a title but could not take into consideration the year and issues covered. Thus the "Shanghai" DB may contain the full run of a journal that also appears in the Dacheng DB where maybe only one issue is currently actually available.
But I still think the XLS-file is a good start to think about pros & cons of these different databases.
You may download the (fully functional and zipped) XLS file here: Comparison XLS, to further play with it and probably squeeze out even more information.
Have fun and please share you findings and enlightenments with us