IMO, if you're looking for power, and spending the cash consider this:
Stock turbos are like $500 each? brand new. SO $1k plus any core charge (but if you have ones going bad send em in and get that $$ back).
CHRA IDK the price on, never really looked at it, but you have to rebuild your turbos for the install correct? So either labor for someone qualified to do it, or you do it yourself and risk messing it up... May add power, may not, but you still have all the limitiations of stock turbo with regards to size, and likely would need to spend more $$ than just the CHRA kit, to properly fully rebuild the turbos... and at the end of the day you have rebuilt turbos with aftermarket parts...
ATPs, have higher MAX power/torque due to increased size. They are BRAND NEW and cost about 2x what stock replacement would, after core charge is sorted out. But you KNOW you can get more power out of them (though you can't max them out without actual engine work to get your 3.5L ready to go).
On a cost to HP ratio, im almost certain that the ATPs are the best option. Cost to performance I doubt they get beat. Hell, on a stock SHO with nothing done, they would get nice gains and put someone right at the limits if they wanted with just the turbos and a tune.
One thing to note...IDK if the CHRA kit can be tuned for remotely, but I KNOW that you need a custom dyno tune for the ATPs. Factor that in...but it still seems like best bang for the buck.
If your turbos are going bad, however, then not sure on engine health or other factors/items that may need replaced/freshened up. Consider all the variables...