you know... I continue to try different things here is what I have tried lately:
slug
blue foam with folded (long way) straw to hold it up
poly fill with folded straw to hold it up
modified rho
mod (looking like a V from the top)
PTB mod that looks like lips on the top
http://www.e-cigarette-forum.com/forum/blogs/rhoneil/408-another-ptb-mod.html
In the past I have used so many things in the past including:
poly ribbon
blue foam and
brass screen
http://www.e-cigarette-forum.com/forum/cartridge-mods/38161-brass-screen-mod-6.html#post590831
and even before these, varying degree, of successes I have tried things that I would not suggest to anyone including (new) shoe laces, and paint brush bristles.
many times I find something that is working for someone else in this forum I try it.
Many times I find that they are comparable to what I had with the FRF PTB mod.
Comparable in vapor, taste, throat hit, initial cart fill and even top off fill.
I find myself coming back to this FRF PTB mod and I think I found the reason.
As vaping just becomes more of a part of my life and no long the only thing Im living for (slight exaggeration) as long as Im satisfied with the basic TVT (taste, vapor, and throat hit) and I dont have to keep topping off every hour or so... what becomes more important to me is the maintenance and topping off convenience.
I have been making rho mods slightly taller than the 510 cart so I no longer need a paper clip all the time to do anything. I can use my finger nails to remove the PTB, rinse it off, dab it dry on a paper towel and reuse.
Because of the spiral in the middle topping off is very quick. I am no longer interested in counting the drops all the time (I still do every once in a while and I get 19 drops in an empty cart and 10-15 drops topping off *results may vary). Usually I just hold the cart on a 45 degree angle, touch the tip of the dropper on the bottom part of the ptb and squeeze until I see it pool in the middle of the mod. I have not been able to top off this easily and accurately with many other mods.
I love the fact that people are still looking for the 'holy grail' of carts and I find myself on here everyday looking for it.
I guess there are people that have found what they are looking for and for them the search is over. Although I realize that what works for one person does not always mean that it works the same for everyone else, I guess what I am saying in this long post is that the FRF PTB mod is the one I still consider my daily, trusted mod.
hope this helps.
rho