Homebrew. Which I've been running for nearly 30 years. For the last ten years, we've been doing 6 hours on a Thursday night each week, and about 7 hours every other Sunday. Previous to that, about 4 hours average per week. So... about 9,000 hours? Maybe take off 1,000 hours to account for "minor" dabbling in Gamma World, Rolemaster, Star Wars D20/Saga, etc. Call it 8,000 hours, then.
...which explains why there's no point in me moving to a new campaign world. Every time our group TPKs, we advance the world timeline slightly. Maybe by a couple months, maybe by 30 years. One of my current players was there for the first session; 30 years ago real-time, nearly 240 years ago homebrew-time. I've seen all of the following occur:
1) PCs who are the children, or grandchildren, or even more distant descendants, of PCs who were played years ago in real-time.
2) One PC who is now the ruler of a major empire, but in a humorous way. His character is widely perceived by the populace as a puppet and a fool, because of silly things he did in his adventuring career. The PC simply lucked his way into the throne by virtual of being the last survivor in a high-level campaign. And now, 10 years later in real-time, the empire's citizens regularly recount stories of his adventuring shenanigans ("Remember when the emperor begged for his life after being ambushed by three hobgoblins? ...have you heard about the time he tried to seduce a polymorphed hag? ...what about the time he spent a day as a statue in a basilisk's garden?). The PC himself has no agency, and has been long retired. But the legend lives on.
3) Nations rise and fall. Heck, the actual geography has risen and fallen on a few occasions, when we were playing particularly apocalyptic / epic campaigns.
4) The stories of the PCs are baked into the mythology of the world. A PC builds a tower or a mine? ...it gets added to the maps. A PC slays a major NPC or crushes a cult? ...it gets added to the history, and will be referred to in future campaigns. The party TPKs? ...their failure has ramifications which often inform the start of a future campaign.
Given that kind of history, the benefits of the homebrew for me are pretty obvious. The players can see the effects of their actions on the world. They are the protagonists, even if their names and roles change every 6-9 months (the average length of one of our campaigns, before it TPKs).
I can't get that with the Forgotten Realms. Joe PC can't kill Manshoon permanently, accidentally open a gate to the Abyss and turn Cormyr into a burning wasteland, then seize the throne of Amn. 45 Realms-years later, the grandchildren of the new King of Amn won't be waging a five-nation war with Thay, only to be betrayed by... [cough] ...anyway, you get the picture. I mean, sure... you can do that with the Forgotten Realms. But, for me, it's always going to feel fake. Ignore for the moment the irony of me claiming that an imaginary homebrew fantasy world is somehow more authentic.
The point is that it's not the real Realms. Every new supplement produced basically tells me: that's not what happened. Your players didn't do that. In the Year of the Disgraced Comedian (or whatever it is in the Realms Reckoning; I've honestly lost track), here's what actually happened according to the latest module/novel/CRPG. You can't see your new tower on the map. You're not listed as the ruler of Amn. Some world-sundering event occurred, but you didn't have a hand in it. Your PCs are not actually the heroes. They're there to impact things, sure... but only on the edges. After they're gone, there will still be a Waterdeep, never fear. And Szass Tam. And Drizzt. There will always be a Drizzt.
So: Go the Homebrews! It's a lot of work, but it's worth it for everyone. I'll happily pillage Forgotten Realms supplements for adventure ideas and other cool things, but I'll be equally happy to never see another campaign setting released by WotC as long as I live. I'm actually quite pleased with the current Adventure Supplement strategy. It's a better use for my money than the fifth iteration of the same-old / same-old campaign setting stuff that everyone can download and re-use from 1e/2e/3e/4e (personal advice: get the 3e version of the Realms... that hardback is awesome).
[...and, final thought, what would be my answer if I had to pick an existing campaign setting to start anew? Planescape. Punk tieflings + smiling fiends + aggressive philosophy + infinite staircases + tripping the astral = awesome]