Finding a 1st edition D&D manual is rather impressive nowadays. From my understanding, those rulebooks are rare as hens teeth. Your main options if you go the D&D route are 3.5e and 4e.
The current system in-use is 4th edition (4e), but playtesting has been happening for 5th edition (D&D Next) for some time now. The edition most people think of when they think of D&D is 3.5. If you're going to go for that edition, though, I'd suggest taking a hard look at GURPS instead.
GURPS was essentially designed to be an upgrade for D&D 3.5 users when Wizards moved on to 4e and left 3.5 by the wayside, and so unlike 3.5, it's got ongoing support from the publisher. Also, it was designed to be compatible with D&D 3.5 material, so you can use modules and other rules that were designed for 3.5 with a minimum of trouble and a maximum of flexibility.
The one caveat with aiming at D&D is that it's extremely focused around combat and fighting. That's where the majority of the rules are centered, and though you can do other things with it, that tends to be the focus of most games, just because that's where the rules are. "When you have a hammer..."
I leave it to the others to offer you advice on other systems. My practical experience doesn't really let me weigh in on that matter.