I would go with Michelin's based on their reliability, reputation, and overall feel. I would rather pay more and know that what I bought is quality stuff.

 

I just bought a used 2008 G35 that has Michelin Pilot Sport tires. They have roughly 20k miles on them and I must say that they are the loudest tires I've ever had on any of my cars. The previous owner was very meticulous about this car and gave me all of the service records showing that they were rotated on time, etc. Yet he told me ahead of the sale that they've been the worst make of tires he's had on the car since it was new.

So I'm in the same boat you are, shopping for something new. I had Bridgestone RE960AS tires on my old car, but they don't come in the right size for the G35. I'm thinking of trying out the Kumho Ecsta LX Platinum.

 

UPDATE: i've had the LX Platinums on for about 25K miles, now. the fronts are wearing very evenly and probably have another 10-15K miles in them. the rears are starting to wear on the inside and the inner wear bars are just about even with the tread. also, the inner sidewall is doing kind of a weird belt shift cupping thing i haven't seen before. they still ride smooth and quiet. the outer wear bars on the rear are similar to the fronts.

i will probably have them dial back the negative camber a bit in the rear and then replace the rear tires sometime this summer. thinking of putting the same kumhos back on as have been pleased with this tire w/ my driving style (see previous post in this thread).

overall the kumhos are a good tire for the money on the 6MT sedan.