I voted T25.
I am a little tilted that you have different numbers of T25 and T100 in this set which makes it tough because most base T25 starting stacks have equal T25 and T100. (ex 8/8/4/x, or 12/12/5/x)
So as your set sits, you can do 20 stacks of 8/8/4/x with 40 T100s left over that do you very little good.
If you add 20 * T25...
It takes you from 20 stacks of 8/8/4/x to 22 making better use of your T100, only 20 extra now, but now you don't have enough T500.
It also takes you from 13 to 15 stacks of 12/12/5/x, but still 20 extra T100 (but at least enough T500 in the set)
If you add 20 * T100....
It makes no sense because you already appear to be overbought on these. If you could add 40 of these, then you would have enough to do 20 x 8/13/3/x stack, but then then that leaves you with 20 too many T500s.
If you add 20 * T500....
You have enough for 20 stacks of 4 or 15 stacks of 5, which are your capabilities leaving T25/T100 unchanged. So I don't see a reason to add these.
If you add 20 * T1000...
You already have enough for 7 per stack plus some extra for color up, I don't see a reason to add these.
If you add 20 * T5000...
You already have enough for 2 per stack to play T20K and still plenty for rebuys, I don't see a reason to add these either.
I'm going with T25 by default. But I think the ideal answer is to additionally remove 40 of the T5000 and add 20 more T25 and 20 more T500 in it's place. Then you have 200/200/100/160/100 + 40 ND, absolutely perfect for 25 stacks of 8/8/4/7 or 16 stacks of 12/12/5/6 (and two "bonus" stacks of 4/4/7/6)