Which manual transmission should I use?

I drive an 04 Honda Accord 5 speed with 212,000 miles. What difference will it make if I use an oil other than Honda gear oil. Some people on various Honda forums recommend Amsoil or Synchromesh or others. I just replaced it yesterday with Pennzoil Synchromesh, but my mechanic expressed concern about this. What is your experience, and what do you recommend?

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