I created an image version of the nuclide chart from Wikipedia:
(You can click it for a larger version – it is actually readable if you zoom in.) There is no date listed there, but I would guess that it is not too old.
By counting, I then found these largest values (I use the index $_s$ for "spread" to clarify that I refer to the width/height or number of columns/rows at that point rather than an actual number of $Z$ and $n$):
- $Z_s=21$ for $n=62, 53$ and $65$
- $n_s=33$ for $Z=36$ and $37$. These are Krypton (Kr) and Rubidium (Rb).
Tin (Sn, $Z=50$) has $n_s=28$, even below Mercury (Hg, $Z=80$) which has $n_s=30$ as well as Tellurium (Te, $Z=52$), Xenon (Xe, $Z=54$), Caesium (Cs, $Z=55$) and Gold (Au, $Z=79$) which each have $n_s=29$.
So the nuclide chart is widest at $n=62, 53, 65$ and highest for $Z=36,37$. Note that I didn't count the number of cells, but the number of filled cells to determine the extrema.