Insulin is a far second.
It's potassium.
Interesting paper but what are you saying. Your linked paper only mentions potassium in the "during the hyperglycaemic phase when the hyperglycaemic induced osmotic diuresis leads to thirst and polyuria" section and it is talking about diabetics and here the sodium losses are 30 times greater than potassium so would consider more important.
If you are answering "I understand to be directly involved in making sugar absorbed in my tissues? I am thinking you are talking about insulin ushering sugar into the cell"
Then insulin is not required to get glucose into the cells from the paper
"This cannot be reconciled with the concept that
insulin is required for glucose uptake by insulin-sensitive
tissues. Indeed it proves beyond question that insulin is not
required. We now know the detailed mechanisms involved
and can explain this. Glucose uptake by all cells is by means
of a specic transport protein (glucose transporter) of which
at least six isomers (Glut 1 to Glut 6) are known"
but I don't understand your reference to potassium can you explain please.