I've known a number. Definitely nothing to set them apart from the crowd. They have really ranged the whole personality spectrum. Some have been quite mentally imbalanced, but in typical Watchtower doublespeak they would dismiss the nutty as pretenders, and the nice ones as genuine, hence perpetuating the myth that they are "lovely people." They have not spoken to me much about heaven, but when doing so it was no different than when the average JW speaks about their fantasies of paradise earth.
If you want to see the answer to your question, look no further than the Governing Body, which contains quite a range. In general, "lovely people" would not be something that springs to mind to describe most of them.