2007 Mazda 3 2.3L GT Hatchback Manual Trans Oil???

Hey guys, i just bought my 2007 Mazda 3 2.3L GT Hatchback with a Manual Trans, and im doing some maintenance on it like, replacing engine oil, oil filter, air filter, spark plugs and manual trans fluid. Ive been reading on many different forums that some oils are good and some not so good:( and would like to make a decision soon.

Whats your opinion on the manual trans oil? For this trans it takes 75w-90 or GL-4

please leave a product link if possible.

Thanks TM3

UPDATE

I went to the dealer today and he says that all they use is 80w90 in their transmission fluid changes.. wtf is going on i dunno whether to believe this guy, the book or people on forums... i really need some help here. What do you guys put in your trannys?