I'll ask the sort of obvious,
Which one feels best to you? Since you are talking the same cartridge in each, no significant performance difference. Some of us prefer the single action grip style to the double action. Bigger issue there than the DA shooting ability of the SRH/RH as I can't see a 7.5" gun with a scope much of a "defensive" set up. With some practice you should be able to get an aimed second, third shot off just as quick with a Single Action as with the Double Action, especially with a hunting level .44 mag load.
If you want a scope I don't see much sense in a VACQUERO. The Blackhawk Hunter and Super Redhawk have the scope mount built in. You did not mention it but don't overlook the "Bisley" style grip option on the Blackhawk Hunter. Many think it is better for recoil control than the traditional "plowhandle".