ex PSA pop data and long term eBay sales data strongly suggests that TMTA had the lowest print run of any EX Series set.
Regardless, I can tell you that TRR wasn’t the lowest print run set like some have stated. It’s scarcer because it’s the most popular EX Series set by a large margin. But anyone suggesting it’s the lowest print run set is wrong.
Some other relatively low print run sets are Deoxys, Dragon, and Emerald. Any of these might be the lowest print run set, although data still suggests that TMTA is (and it’s not particularly close).
And this is just re: the EX Series. It’s very possible that Skyridge had a lower print run than any of the previous sets mentioned. No one knows for sure, but it’s certainly the rarest WotC set.