The one with the original cast What the reunion proved is that the chemistry is still there and it would be crime to let it go to waste and just sit on the couch. The brilliance that the writers and casting team managed to put together is just to rare. I wouldn't mind watching a Friends universe expansion where we follow a modern day 20 something year old people managing their lives. The spin is that their parents are more involved then it was in the 90s and some of the kids could be even living in their parents basement or driving them around. And you guessed it, the parents are the original cast of the Friends who have moved on with their lives in the past 20 years and could have evolved into new personas, some less, some more so. The original show would be kept untouched. New show skips 20 years and looks onwards from that point on, on themes of being in your 20's and also 50s today. That way the show keeps the original chemistry and adds some energy with youngsters. We would just need one more miracle casting :)
The possibilities are endless though, some of the kids could be seeing each other which means they would be having occasional dinners with both of their parents. Some of the parents could be neighbours and so on, so on, the possibilities are endless to keep the original cast on one screen. The show shouldn't be called anything Friends though. Anyway, just putting this thought out there, you'll never know. Put mainly it's just wishful thinking.
Let's be friends forever.