Hi,
I need an Arduino with Ethernet port built in like the Leonardo ETH. Leonardo has been retired and now I don't know which one I've to buy.
Thank you.
There is a new MKR series board with Ethernet which is both breadboard friendly and much better than the Leo ever was.
There are also Ethernet shields / add on's for most of the other boards to allow the features you may need.
The YUN also has Ethernet.
If I were just starting out the MKR would be my board of choice for Ethernet.
There is a new MKR series board with Ethernet
Very new indeed. "Available soon"; also, this appears to be a MKR format "shield" rather than a board with built-in ethernet. See this thread: Arduino products with Ethernet - Products and Services - Arduino Forum