You know, the extra cost of the Havana is easily offset by the cleanliness of it being silicone and the veratility of having a vibrating bullet. It would probably make a pretty easy plug to use for a beginner.
Both are made of silicone, so material isn't an issue. Vibration definitely adds something different into the mix. I have the Buddy and it's great, but it slips out. I think the Havana probably would stay in better because it has a narrow neck.