Bookmarks
Streamtuner2 allows to bookmark favoured streams/stations. Which is what the bookmarks tab is for, of course.
Use right click for a stations context menu ▸ bookmark or just press F8.
Once bookmarked the station is listed under bookmarks ▸ favourite. Additionally every appearance of the station in channel tabs gets a ★ star icon.
Editing
Entries can be removed from the bookmark list again. Use Edit ▸ Delete or the DEL key for that.
You can also manually adapt an entry via Station ▸ Edit or by pressing F3.
Subcategories
The bookmarks tab can display other categories besides "favourite". For example the search feature creates a "search", while the "timer" and "links" plugins also display lists here.
However the favourite list itself can not yet be categorized further.