bmw's handle weird(IMO), lexus=toyota with leather, infinity=well bad.
so i guess that leaves you with the audi which is realy the only not gay choice
Honestly I would lean towards the G35. Out of the group its going to be one of the better drives and IMO look sicker, all they need is tint and those car looks 10x better. BUT ONLY THE COUPE.
You mentioned that only the G is 6spd. So if that is the only stick car, def get the G its cheaper and has less miles then the others to.
Otherwise I personally would go towards the Lexus (always liked that car very reliable and classy with a sports look) or the A4 for the AWD capabilites, they look sick, reliable and fun to drive.
Keep in mind that you may be dropping the 20 grand now for these cars and it may seem really affordable, But all these cars when they need to be repaired will cost you a huge chunk of cash just because of the name.
for ex. BMWs have problems with the window motor ( it gets junk stuck in the mjotor and you cant put down the window or its stuck down) it happens within 60k miles sometimes even 30k. And thats a few hundred dollar fix. another ex. I own a John cooper works, BMW made, and when i needed a new power steering pump it was about 750, and my new struts all cost me about 1.5k
Just keep that in mind for the future.