There are a couple of differences that can best be found out in comparing
http://www.logos.com/originallanguages /
http://www.logos.com/comparison with
www.sesb-online.com. The most important differences are:
- Number of resources in library: SESB comes with about 50 resources the Original Language Library with about 200
- Critical apparatus: Only SESB provides the critical apparatus on BHS, NA27, UBS4, LXX and Vulgate. The Original Language Library only has the overtext of these resources.
- Both, SESB and the OLL include morphological databases on the original language texts. In addition SESB features the syntax search in the WIVU database for the BHS. The OLL includes the Anderson/Forbes database on the BHS instead.
- The OLL comes with Reverse Interlinear Resources, that are helpful if you don't know Hebrew and Greek (well) and want to access the original language texts from the English translations. SESB is better designed to work the other way round: To start with the original language texts and to access additional information from dictionaries and databases for translation and exegesis.
Summary: Each of the two has advantages over the other. It really depends on your interests which one is the better choice for you. In fact: The best choice certainly would be to use both in combination.