"strongest partner" is a correct and usable phrase in written English.
You could use it when referring to a strong connection with someone, for example: "Jessica has been my strongest partner in life."
The Khmer Rouge was the strongest partner in this coalition, which carried on guerrilla warfare until 1991.
"To suggest that Paris and not London is Washington's strongest partner is simply ludicrous," said Dr Nile Gardiner, director of the US-based Margaret Thatcher Center for Freedom. US-based Margaret Thatcher Center for Freedom
With 17 participations, Kazakhstan was the strongest partner from this region.
Most pundits assume that Microsoft will swoop in and help Nokia out if things really go sour (after all, Nokia is Microsoft's strongest partner with regards to Windows Phone).
Fermilab considers Italy its strongest partner country, according to information provided by the laboratory.
In a statement, he argued that "the United States should stand for self-determination for our strongest partners.
The Yorns had been viewed as the strongest partners in Mr. Ovitz's company, with powerful relationships among the stars.
Some of our strongest partners are in the corrections community.
With high-quality training, LSCs can be your strongest partners in school reform.
He exhorted fellow Republicans to be Obama's "strongest partners" when they agree with him.
China, he said, was the stronger partner.
