Second last option.

Robin should be Dick Grayson and Batman should bang Catwoman.

Wow, interesting way to turn tradition on its head.

Hasn't that already happened?

I don't think Catwoman ever assumed the Robin mantle, no.

Right. Just the banging thing.

The correct answer is the Dark Knight Works Best Alone.

• having Kid partners really only works in 1940s and 1960's TV shows.

Right there in your opening post. Gosh, yes, Batman.

The ideal Robin is Dick Grayson with Tim Drake attitude.

Absolutely!

Tim Drake and Carrie Kelly are why I can't get on board with the "only Grayson as Robin" train.

Ideally, Dick would be Robin until he grew up and became Nightwing. Then Batsy, having learned that he didn't need to be the lone dark brooding avenger of the night, would continue his fight against crime, while just as fearsome and foreboding to criminals, but more at peace with his internal baggage.
Dick will have helped him deal with all of that, and gone on to make him proud by becoming a great crimefighter in his own right.
No need for a continual supply of Robins. At least if this was "real life"
But as we know, DC has to maintain the copyright on the character, so, we get a virtual Robin-rama, with a new one every few months or so..

Ideally, Dick would never grow up and Nightwing would be in the Bottle City of Kandor.

But he did, and there have been many wonderful stories because of it.

The following conditions are, IMO, the best single state of affairs:

1. Robin is Dick Grayson, first and only ward of Bruce Wayne
2. He's about 20 -- been with Bruce for years and grown up, but still young. He never becomes one of the older characters -- he's poised at the very start of adulthood.
3. He's the leader of the Teen Titans -- the only one without powers, but a game-changer with his leadership (a la Steve Rogers). He's actually the anchor of the book, the fixture that never changes while other "teen" characters get tried out.
4. He still has adventures with Batman on a pretty regular basis -- there's a separate title called "Batman and Robin" for people who enjoy these stories.
5. It's fully understood that Batman does a LOT of things solo -- Detective Comics or other titles would be devoted to solo adventures.
6. He can have a different costume, even play around with other names (like Nightwing), but it's not because he's leaving, butthurt, or to make room for other Robins.
7. His leadership of the Teen Titans, and growth as a character, makes for a nice contrast with Bruce Wayne -- Bruce grows a little broodier and aloof as he's aged (some would say darker), while Grayson grows into more of a "I believe in the light" kind of guy (Steve Rogers). It makes for some "I'm not like you" moments, and we see Grayson as more the "Knight in Shining Armor" instead of the Dark Knight.

Robin should not be a member of the Teen Titans unless he is a teen. At least make him 19 and not 20.

Dick Grayson and the rest of the Teen Titans work best between the ages of 13 - 16 for me. There needs to be a certain learning curve for all of them, not just about being a superhero, but about life as well, and this includes Dick Grayson. For me, anything above 16 is more like a partner than a "sidekick" and I like the idea that they become more that sidekicks when they work together. It was the basis of their creation.

I think Dick works best as the 45 year old leader of the Teen Titans and the boss of a 8 year old Batman.