My three kids have been to Peter Pan, Simba Club, and the Cub Den.
Hands down, Peter Pan is the absolute favorite with the kids. They LOVED, LOVED, LOVED it. In fact, they begged us to go out another night so they could go back (we did not do it though, it is darn expensive for three kids! - for the <ahem> alone time we had while the kids were at the club, I felt like a high priced - you know what!

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I am not sure why the PP club appeals to the kids so much, maybe its because of the 'climbing through the window' thing, or maybe its the crafts, or maybe its the cm's. I will say that it appealed to ALL my kids too, which I found shocking, as my 10 year old (going on 18) loved it just as much as the younger two. We took them here on two different trips, first time when they were 5, 6, 9, and then 6, 7, 10.
Simba's club - my kids said they did not enjoy it as much as PP. They were a little older on this trip, so that may be a factor. Also, they prefered the 'buffet' dinner set up, rather then 'ordering' a meal at the Simba Club. I also thought that the room was much smaller then the PP club, but I could be wrong on that. We took them here when they were 6, 7, and 10, we wanted to try Jiko (amazing restaraunt!!!)
Cub Den - my youngest two stayed here at ages 8 & 9. They were ho-hum with this club, they liked it, but did not say they had a great time, or ask to come back. They begged very hard to do Peter Pan, infact the 13 year old said she wanted to do Peter Pan if that is where the kids were going - I told her she was too old, she didnt care!
That is just my impression of the 3 clubs based on my kids attitudes on them. All the CM's at the three clubs looked very personable and enthusiastic. I am not sure what the heck they do at the PP club, they must sprinkle the kids with pixie dust or something, they didnt want to leave, and they talked about it as one of the best Disney moments for them. If you are eating at a monorail resort, I would highly recommend the PP club for you. Just drop them off on your way to the restaraunt, and pick them up after. Its easy to do on the monorail. (If you are thinking of alonetime with your spouse after the meal, consider taking cabs to your destination. The time you save on transportation will more then offset the cost of the cab if you have two or more kids in there)