IMO depends how high exclusive lvls are your partners. If it's low then get exclusive frags but if this 1000 frags would give you for example only 1 or 2 exclusive levels then it's better to go for stones
A good choice to make sockets, if you have firelord set.
With the improvement of armor, you will need more material
for firelort set 2 socets = ( 2+4 ) *6 (24 for cultivation)
same for dark set = (6(not shure)+12 )*6 (only 20 for cultivation)
and so on