3DS versions of both games? I prefer Lost World. Not only does it have more content, but it's also more polished. However, Generations (3DS) is almost exclusively, 2D and features many modernized Zones and bosses from previous Sonic games, such as StH1-StH3&K, Sonic Adventure 1&2, Sonic Rush, Sonic Colors (DS) and even Sonic Heroes. You control two different Sonics: Modern and Classic, seperated between Act 1&2. Classic Sonic plays similar to how he did on the Genesis titles. (Although, it lacks most of the momentum based physics.) Modern Sonic essentially plays similarly to how Sonic plays in Sonic Rush, minus the ability to SpinDash and the lack of "Air Tricks". The only 3D portions that Generations (3DS) has are the Special Stages and the true final boss fight.