You should experience both. To distinguish between the two qualitatively, in words, is difficult, as what each person gets off on isn't the same. Let me (imho) opine as follows: the 6th floor are reasonably doable great-grannies and you go there for the price and the fact it is just nasty (nasty being part of the appeal for some). No frills, doing the deed, most anyway you want, NASTY.
3rd floor has easier on the eyes almost grannies that have more enthusiasm for performing the deed and are aware of nasty and contribute to it through their acting, rather than just being. There is also the possibility of a good massage, a hot double, and extended play. You pay a higher price point in return.
On balance, both provide equal value for what you spend and you will travel home having been and feeling nasty and in need of a shower. Both provide an experience that you might relate only to your best friend, though more so the 3rd and not the 6th.
Does that help, lol ?