Logseq has a daily journaling workflow built in which you can sort of automatically grow into a kind of personal wiki. It also has built-in flashcards. However, the pages are very generic and formatting is limited.
Obsidian, on the other hand, is more of a "blank book" that you can turn into anything that Logseq can do. It has richer formatting and a _huge_ collection of plug-ins and templates are available (including flashcard plugins). It supports math markup, diagrams and inline tables. There's a "Webpage HTML Export" plug-in for publishing to the Web.
Both offer canvas/whiteboard pages and are completely offline, by default.
So, for power & versatility, I'd go with Obsidian. If all you want is a journal and flashcards study tool, Logseq might be simpler.