While both of these legendary creatures are great, I think Tidus is the better option
To this end, Ive done my best to prepare the most logical argument on behalf of the much-maligned Land Destruction player
If Static Net leaves the battlefield before its first ability resolves, the target permanent won't be exiled
Morophon was an obvious reprint for the Eldrazi Incursion deck, where it pumps your Eldrazi creatures and makes Ulalek, Fused Atrocity free to cast
On the other hand, there are some non-Niv decks in older formats that could probably use Jegantha, the Wellspring, the question is whether starting with a random 5/5 for five in hand is the best use of a sideboard slot
Last I recall, payoff and token production on the same commander is a pretty good combination of effects