The only wild species I have seen is L l lutra in England.
In captivity I have seen and photographed these barang+ giant, North American, Oriental small-clawed, smooth and spot-necked (I have just scanned photos of these last two - watch this space); I also saw Cape clawless at Basle in 1972, but as they were asleep I didn't bother to take a photo
Perhaps one day I'll see wild sea otters.