The bibliographic databases have a transparent search system and contains almost exclusively publications that are quality controlled.
LUBsearch has in many aspects similar attributes to the bibliographic databases. An advantage with LUBsearch is that beyond academic publications you can find many other document types such as reports, book chapters and news articles. A disadvantage is that the result list often contains duplicates. LUBsearch searches simultaneously in several different databases that Lund University has access to, which you need to present (see Databases A-Z).
In Google and Google Scholar you will get more search results as they will generally search in the full text, not just the bibliographic information (title/abstract/keywords etc). In some cases this is a huge advantage. The downside is that you have little control over your search (these search tools have a sort of "hidden help"), which makes it non-transparent. Boolean operators (AND/OR/NOT) and truncation doesn't work well. Furthermore, the search you do in Google is not repeatable or non-partial as the Google search algorithm will generate different search results depending on for example your search history, the language setting on your computer and the popularity of documents. Google Scholar appears to be somewhat better in this aspect, but it is unclear to what extent. However, as some sources can only be found through Google (aka. "grey literature"), it can be a good complementary search tool. Keep in mind that in both Google and Google Scholar, you may find sources of doubtful quality.