This is a very tricky question, as all of us have used different products and had success or failures with them.
There are lots of different formulas and they can be really confusing, they are basically broken down into several categories.
Gold- these have omega 3's added to help with brain and eye development...no real proof to say that they do.
HA- these have been broken down to be more easily digested as cows milk is a lot harder to digest then breast milk.
AR- these are thicker formulas to help with reflux
LF- these are lactose free for bubs that are sensitive to lactose
Then there are the normal formulas and the speaclised ones such as soy or goats milk based.
I think what you have to do is work out what is going to suit your bub, the availability of the formula you choose and also the price you are prepared to pay.
All formula has to meet VERY strict world health guidelines on the formulation...eg certain levels of vitamins and minerals.
So to answer your question...finally...ther is no BEST formula, you need to find what is going to work for you.
Some companies have sachets of formula, you may want to try bubs on a few sachets to see if she will drink it, so you don't buy a tin of formula she won't drink.