I'm not completely satisfied with TeXShop's internal editor (especially about line breaking), but I would like to keep using TeXShop for its neat visualization engine and sync features (inverse and forward search). Is it possible to keep those functionalities, or at least a decent inverse search, while using an external editor with TeXShop? If so, do you have any suggestions about a suitable editor for Mac?
Take a look at this page about using TeXShop with an external editor. You can configure TeXShop to open files in another editor, and if that editor can run unix commands, TeXShop provides executables for its interactive compiling.
many many editors support this. Emacs and auctex does with the
synctex package. So does texniccenter on windows.
It's not just for mac... but check out http://mactex-wiki.tug.org/wiki/index.php/SyncTeX