You've Been Watching the Star Wars Films Wrong All Along; Here's The Correct Way, According to Lucas
The Internet disputes on the proper order of watching Star Wars movies are undying in the fandom.
The main contenders in those disputes are the chronological order (the prequels -> the original trilogy) and the release order (the original trilogy -> the prequels), though some fans offer more complex combinations, like Episodes IV and V -> the prequels -> Episode VI.
However, what about the opinion of George Lucas himself? Well, he certainly does have one, according to Vulture:
"Start with one. That's the way to do it right: 1, 2, 3, 4, 5, 6. That's the way they're supposed to be done. Just because it took a long time to film it doesn't mean you don't do it in order."
So, basically, the creator thinks that the chronological order is the correct one.
Yes, it is rather doubtful whether Lucas had a grand plan for the whole saga when he began filming it. In fact, it is almost certain that such plan could not exist as anything approaching its final form, before Episode IV established itself as a smash hit, and work on Episode V's script began.
But those who champion the chronological order do have strong arguments for it (it is almost impossible to find someone, even among people young enough to never watch Star Wars before, who is not aware of the Episode V's big twist; anyone who still has to be introduced to Star Wars in our day is likely to be a kid, and Episode I is the kid-friendliest of them all; etc).
Of course, we're free to interpret movies, once they are released for the public, and we're not bound to share their creators' exact opinions and viewpoints. But on the other hand, a creator's opinion is at least worth considering, particularly in this case.
Lucas received tons of criticism after the prequel trilogy, having to defend all of his creative choices (and even aspects of its creation, in which he really had no choice) from a vocal and toxic section of the fanbase.
The treatment he received from his previous fans was awful, and consequently he felt almost completely burned out after the prequels, despite being financially independent and able to create movies with his own money. If he believes the films are best viewed in a certain order, maybe we owe him at least as much as listening to his opinion.