That will be up to user preference. I prefer the fuel injection that was added in 75, others prefer the carbs in the 70-74's. Basically the car got heavier, fancier and (maybe safer) with the addition of larger bumpers.
The 280Z is the safest due to its thicker metal and big bumpers. the 280Z is also the most reliable because it comes with FI. but the 280Z is also the heaviest. The 240Z is the lightest has the thinest metal and has the smallest bumpers ans it is also the fastest so I guess its the least safe. the 260 is in between the two, but it has evil carbs that arent as good as the 240s.
Basicly the motors are the same except for the fuel delivery. The 240Z has a small bore and a short stroke(revs the highest), the 260Z has the same bore as the 240 and a longer stroke, the 280Z has a larger bore and a longer stroke(makes the most power).
So I guess it all comes down to what you want. if you want flat out performance go with the 240Z. if you want good performance and want to be safer and have better reliability get a 280Z. if you want less reliabilty and performance go with the 260Z(only get it if its real nice or if its all you can find). Or you get a 240Z and drop a 280Z motor and FI and have awesome pefromance and reliability(what I'm gonna do one day minus the FI).
Theres only one choice the 1970-72 240z..... why because its before smog and you can put any motor you want in it from a Silvia S-14 turbo, to a twin-turbo Skyline motor, to a turbo or twin-turb 280zx motor to the all crazy V-8 and then the possibilities open up even wider...... and its the lightest and can be the most nimble to. read this site for yourself and check out one way of making a fast_Z ,...........
It all depends on your needs, If you want a uncomplicated car that is fun to drive and handels like it is on rails and will go as fast as your wallet allows buy a early 240 .Electronics are great and the nultiport injection is fantastic BUT as these cars age and somthing in this complicated system goes sideways you need a catsscan to find what it is. My 73 Has SU carbs a '79 electronic ignition , and runs great. I perfer to be able to work on my own car , it my joy and my frustration and if somthing happends to this one I'll find another 240 with the little bumpers and thinner metal . The cars are classic and look classic a mix bewteen a Jag ZXE , Porsha, & Early Corvette . thats my story and I am sticking to it. This is a vary good web site for information that you are looking for I think . www.geocities.com/zgarage2001/z.html give it a read It is a good down load for reference . 32 pages. Good luck Gary Portland Ore.
hay now come on from 79-83 they made the 280zx <wich to me is the badist z STOCK but i like the v8 240z`s hehe ;0) > and about saying your tall my dad is like 6`2 and he rides in my car < it was tighter with the stock seats but i now have summit raceing seats and there almost to low haha i have like a foot of clearance im 5`11> but hay its all what your looking for also the ZX`s have less rust normaly becuase there newer and havent been around as long..... i think the idea of a 260 was just a goof by nissan <datsun what ever> think they could have put all that efort into a better 240\280 instead of making a car no one really likes....... just my 2c