My favorite world created by the Gurus is probably Twinbrook. The world is gorgeous, and I love to play in the swamp area. But my favorite of all time is definitely Legacy Island 3 by Rflong7 on The Exchange. I mostly play "build the house as the generations come along" legacies, so the abundance of empty lots in all the different sizes is absolutely amazing. But there's also a ton of amazing premade houses that I can just plop my sims into if I feel too lazy to build. Not to mention it having all of the expansions used, so I'm able to play any sort of challenge that I feel like.