Out of those you listed I have the 9, the 6 and the 6.5. The 6 is definitly the most powerful of those, but it is very anatomy dependent, meaning it won't be a perfect fit for every anatomy! It doesn't fit with mine. The clit arm ends up off my clit and so I end up using the internal portion externaly instead of the way it was designed. The 9 is too floppy to put pressure on my g-spot. I like the jejoue uma or lelo gigi better than vr9. So we come to my vanity recomendation, the 6.5. It is flexible enough to work for most women and while I wish it was as powerful as the 6 it is strong enough to get the job done! And I am definitly a power queen!!! I like it best when both motors are at their highest setting! It somehow makes them both feel stronger! Let us know how it goes!