The main difference between tabs and expanders is that tabs remove the old block of content when the user selects a new content block so see, while, with expanders, old content blocks by default remain visible when the users selects a new one. Tabs are thus preferred when the user is zeroing in on a single specific piece of content, and nothing else on any of the other content blocks is of interest. Once the user finds the specific content of interest, they’ve no reason to go to any other tabs. When searching for the content of interest, if the user doesn’t find it on one tab, going to the next candidate tab “automatically” removes the rejected content block, reducing clutter and bulk.
Multiple expanders are preferred when the users are typically interested more than one piece of content in alternative content blocks. This is especially the case if users often return to review content in different content blocks. The user can open all expanders with content of interest and leave them open for reference or comparison.
Tabs versus expanders is sort of analogous to radio buttons versus check box arrays.
User research will tell you how you expect users to use your site, but I suspect that your example web site is probably best with expanders since it seems to be aimed at free-form flexible exploration. For example, a user sees attractive art in Artwork, so looks at events for opportunities to see the art in person. Seeing the artist gives a seminar in Events, the user may want to look again at the art work for techniques s/he might like to learn.
Tabs might be preferred when the content blocks are so lengthy, it would make the page too long if more than one were visible at once as with expanders (e.g., it's easier to click a new tab to see an old content block than to scroll a long to back to it). However, if that’s the case, you’re probably better off putting each content block on a separate page and using conventional links. Expanders can also disrupt the absolute positions of content between or below expanders, so if there is a lot of reference to such content, tabs may be better so the content stays at a consistent scroll position.
I wouldn’t make expanders-versus-tabs a choice for the users. It’s an unwarranted burden and they are not likely going to know the trade-offs to make a correct decision. Only give users choices when they know better than the designer, which is very rare for design choices.
If you expect most users to serially go through all the content blocks in order, then don't use tabs or expanders. Just put all the content on one page, or, if the blocks are long, a series of linked pages.
