I have both mojito and spear mints. I just did a test, and I think the mojito has a bit sweeter taste and smell to it. I have no idea, but my thought is the mojito drink probably came about before the mojito mint -- ??
It says some places that Mojito Mint is "endemic to Cuba," which can't be true because I believe the mint came from Europe to begin with. But I'm willing to believe that Sir Francis Drake had a drink made with proto-rum, Cuban limes and mint found in Cuba and it was later called Mojito, and then "Mojito mint" is marketed to people like me!
I realize the last comment posted on this thread was done over a year ago, but I just bought a beautiful Mojito mint plant from The Gardeners Exchange. I ordered a new spearmint at the same time, and I'd have to say the Mojito has a much more citrusy scent than the Kentucky Colonel spearmint. Hope all of yours are growing and happy!