I've tried a lot! My favorites are the Mini Luna Beads. I've shared the differences & why I like these and dislike the others many times, so I don't want to get that lengthy here, but if you check around the forums (by doing a search in the search bar using those key words in your own thread) you'll find a lot of really helpful discussions. I like the Luna Mini's because I require a smaller ball than the average ones & there aren't but a few small kegel balls available. I think they're actually the heaviest available - - if you combine both blue balls in the kit. The regular Luna beads are identical, only a LOT bigger.
Hope this was helpful for such a brief post. I hope you'll read other's discussions here in the forums on this topic too.