Lowest threshold?
 

Which *Alliance FFP have the lowest threshold for Gold status??

For annual renewal, AC is 35K.

Technically correct but TK actually has lowest for renewal

40K in 12 months for initial entry is higher but
for renewal
only 30K/45K (Turkish residents) in 1/2 years
or 25K/37.5K (non Turkish residents) in 1/2 years

The actual number is not that relevant. The OP also needs to take into account how many miles he gets for the flights he will be taking.

It can be as easy to achieve the 100k miles for LH *G than it is to get the 40k for OZ (which gives almost 4 years of *G).

Completely agree... For example many state BD is an easy programme, however in Y it is probably the hardest in *A. At the end of the day, it's horses for courses.

BD is not anywhere near the hardest if traveling in Y if you're traveling below a certain threshold of miles per year, because for some programs it would be impossible to ever even reach *G. For example someone flying only 39K per year could never even reach *G with some programs but with BD your status/qualifying year reset at each level. So even though you need more than 50K to go from zero to Gold it is still doable with such a low level of flying per year. It will take one and a half years, but it is doable. Other programs which are based on a fixed calendar year aren't as flexible in this respect so aren't of any value to some who don't fly more than say 50K in any given calendar year.