What is better? Use the Tiled application or Unity TileMap and use 2D-Extra. I mean in the sense of performance.
I believe it shouldn’t matter in terms of performance. At least if you’re using SuperTiled2Unity then the tile map you made in Tiled will get converted to a Unity TileMap asset as far as I am aware, so in the end it’s the same thing.
Maybe @Seanba has more to say about this.
I’m not really sure as I’m not too aware of the 2D-Extra scripts and what they do. Both are probably similar in terms of performance and I guess it comes down to the kind of maps you make.
In my experience people starting off fresh tend to make large maps with lots of layers and objects and then try to get that map exported into Unity which I think is a painful way to go about it. So, start off small, build up from there, and get a sense for performance as you go along. This advice applies no matter which tech you use.
For me, personally, I use Tiled because I find it painful to use Unity as a tilemap-editing environment.