I want to start and (this time) finish the two Asimov series I have: the Foundation books (trilogy in fact) and the Robots cycle.
Is there a particular order between those two series or are they totally unrelated and can be read in any order?
I think that neither published order nor chronological order quite does the series justice. Here's the order I think makes the most sense for maximum enjoyment of the books. You'll notice that I've left some out.
The series was never quite finished, so I feel that a non-linear approach is the best choice here. This allows one to emphasize the building of themes within the books, rather than individual plot threads.
At their heart, these stories work best when they focus on individual people. This may sound odd, as the robot and Foundation tales are meant to illustrate great sweeps of history, but in my opinion, the strongest tales here are those that are small and intimate. Think of Susan Calvin and the Mule and you may see my point.
I've left out the two prequel foundation books that Asimov wrote. While they're good, they do very little to add to the fabric of the story, and can be viewed as bonus reading material for later on. (If anyone disagrees, please tell me why; I'd be willing to reconsider this point, but haven't read those books since they came out.)
Similarly, the three "Empire" novels, set in the very early days of the Empire--they're not up to the level of quality that the other books achieve, and can safely be read after finishing the main series--if at all.
Other books, like Roger MacBride Allen's "Caliban" novels, can be enjoyed off to the side, as they don't really forward the story arcs of the rest of the series.
Rationale for this order is below. Spoilers for those who haven't read the series.
"I, Robot" is a short, fun read, as is almost everything Asimov wrote. It was the first book of Asimov's that I read, and it's a great introduction to his work.
Next, jump ahead in time and read the "original" Foundation trilogy.
The reader will notice immediately the lack of robots in human society--what happened to the robots during the thousands of years in between these books?
We see the harm that robots can do to a society where they are forced to preserve human life at any cost.
Somehow, Daneel Olivaw has been behind the scenes for years. But how was this achieved? We'll find this out in the next book.
Since Asimov never finished the Foundations series, this is the closest thing we have to a climax. Which is why I placed it here, and not after the Robot novels.
The promise of humanity's future is a noble, optimistic one that we know will pan out imperfectly. The grand vistas of time stretching out at the end of this book show us that human history is cyclical, and that the nobility of human achievement is in the very act of us striving for something better.
I've done it both ways and preferred reading in chronological order, except you want to include the empire series between the robot and foundation series. There's a lot of time between robots and foundation and the few short books of empire take place during that time. It gives a better understanding to how Earth was lost.
I like to look at the series as the story of R. Daneel Olivaw, which results in me having a different order than most. For the sake of simplicity and focus, the robot short stories, the Empire novels, and the Caliban trilogy are left out as interesting, but non-essential.
First, the four Robot novels should be read before the Foundation novels, in chronological/publication order:
A) The Caves of Steel
B) The Naked Sun
C) The Robots of Dawn
D) Robots and Empire
After the Robot novels come the Foundation novels: seven by Asimov, plus the Second Trilogy by Benford, Bear and Brin. Some include the Second Trilogy, others don't. I prefer to include two of them, as I find they improve the overall story of Daneel. Foundation's Fear by Benford can be skipped entirely; it's disrespectful to the source material, adds almost nothing to the overall story, and is just not an enjoyable read.
As you said, the two common recommendations are to read these either publication order or chronological order. I have a third recommendation: start with the original trilogy, then read the prequels, and end with Edge and Earth.
B) Foundation and Empire
C) Second Foundation
D) Prelude to Foundation
E) Foundation's Fear (if you really must)
F) Forward the Foundation
G) Foundation and Chaos
H) Foundation's Triumph
I) Foundation's Edge
J) Foundation and Earth
This gives a good arrangement stylistically, with the earlier novels followed by the later ones. Asimov's writing style changes distinctly over time. It also gives a good arrangement chronologically, with the prequels foreshadowing the final two books, instead of explaining things you've already read about. (This can be compared to the Machete Order of viewing the Star Wars movies. But I digress.) And best of all, you end with the cliffhanger, instead of reading it and then reading 2-5 more books that don't resolve it.
And if the cliffhanger bothers you, I wrote a conclusion which seems to be well-liked.
They start off unrelated.
However they start to converge in the last few sets of books. I forget which ones specifically (5th Foundation? The one after Foundation's Edge I think). Sort of like Heinlein's universe-as-fiction notion to unify all his books. But Asimov did it a little bit cleaner I think.
An order that has been working for me was to start with the End of Eternity. That's give you the basic understanding of how and why the galactic empire comes to be. Then I started The Foundation all the way to prelude. I read prelude last to give you More back story on Hari. Because of the reference to the robots in the last few Foundation books, I feel it brings a lot of exciting tie-ins when you start the Robot series. From there I read the Empire series. And then I finish at Forward to Foundation.
My dad gave me the books in a specific order. I read the Robots books first (the series with Daneel). Then I read Foundation, Foundation and Empire, Second Foundation, Forward the Foundation, Foundation's Edge, Foundation and Earth and lastly I read Prelude to Foundation. I liked this order but in hindsight I would have re-read the first few Foundations before reading Prelude to Foundation, just to refresh my memory. I read End Of Eternity somewhere in between the Foundations but I don't really think that matters, beacuse it is not explicity linked with the Foundation universe, or it is not necessary to the storyline to understand this link.
I'm going to recommend my own personal hybrid, partly based on the order the stories were written, and partly the internal chronological order. In my opinion, it gives a better sense of the development of the story and Asimov's direction than simply following the chronology or the writing order. Also, I think it's compulsory to read 'Forward the Foundation' last. Asimov "ended" the series by taking it back to its beginning - I think it's a nice touch. Also, the final scene in this book is a nice way to finish.
The Caves of Steel
The Naked Sun
The Robots of Dawn
Robots and Empire
The Currents of Space
The Stars, Like Dust--
Pebble in the Sky
Foundation and Empire
Foundation and Earth
Prelude to Foundation
Forward the Foundation