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I take it since you mention the fact that it's a manual that your refering to the oil in the transmission. Either way I would use synthetic and Mobil 1 is also my preference, but if your going to use a regular oil then Castrol GTX is the my choice.
According to BITOG oil analysis samples, if you change every 3000 miles then any GF-4 rated oil will serve you just fine. If you do race then by all means goto a Synthetic. If you like to go towards 10K miles then also your need Synthetic. Brands, my best performance so far was Pennsoil Platinum.
Just a bif whoopie. Heck believe it or not at 3000 miles or less the walmart SM GF-4 graded super tech is just fine for long engine life. Name brands stuff has some very minor advantages but not that is shows up in an oil analysis.