For my money, I love fuel injection. In that vein, the '75 through '78 280Zs are all good bets. They're basically the same body shell and suspension setup with minor changes ('75s had no hood vents; 75-76s had full size spares as opposed to inflatable ones in '77-78s, 77-78s had cooler looking bumpers, etc.) By '77-'78 Datsun also offered 5-speeds, which are a step up from the 4-speeds in the '75-76 cars. Of course, almost all the mechanicals (rearends, motors, trannys) are interchangeable, even the turbo motors from later ZXs. And while we're on the subject, don't count them out. They may not have been quite as sporty as the first generation Zs, but they were cool cars in their own right. I presently own one of each, a '75 and an '82 turbo.
Look for a 81-83 base model ZX Deluxe with manual rack and pinion and roll up windows. Much simpler and easier to maintain than the heavily optioned cars. Lighter too. Almost like a throwback to the orginal Z. I used to have one but I don't think there are too many around.
I would say go with the body style that suits you. I used to own a 79 280zx which was a nice car. I loved it. I now own a 75 280z which is my favorite of the two. The zx had a more luxurous interior and was more passenger pleasant meaining it was meant for comfort. The z however is still comfortable but it seems to be made more for the driver experience. Both cars had a rebuilt motor and (in my opinion) the z gets up and goes where the zx was still getting up. I would stay with fuel injection. I have had other cars of other models with a carburator and I prefer the injection anyday. My favorite is definately the z! Also take your time in deciding and choosing a good one.