I'm currently looking for a car that is sporty, has 6 cylinder s(gives around 20 highway mileage), is luxurios, and also has good safety rating. My plan is to hand it down to my son next year when he turns 17. What's a good choice out of these three or is there any other luxury sports car that meets this criteria.

the M3 is the best of those rides - period. The problem is ...used ? just need to do your due diligence and checking how well it has been cared for. Also, handing a car like that to your 17 year son ( well nice ) will probably lead to trouble. I got in trouble at 18 with a modified honda civic !!! None of these car are great for new drivers to be truthfull...
You will not get the techy stuff that the Lexus and infiniti have in them but you will have a better preforming and handling vehicle. I love and own infiniti's but I think the Lexus has a better look than the G37. All things being equal - for yourself, I would go with the M3, Infiniti, then the Lexus in that order - as for a car I would give my son at 17, I would go in reverse order... ( Lexus, Infiniti, BMW )... see link for comparo...

If u want to keep ur son out of trouble(and on a more serious note) alive, then dont give him any of these cars. Aside from the m3 these are 300+ hp cars. If u trust him thats one thing. Go buy him a well taken care of, safe, good car and get urself an m3 or IS 350.