vacuum advance

With cams smaller than 232*@050 I find the spark port preferred. as the cam gets bigger it can go either way for awhile and after 250, I imagine the extra idle timing might be welcome by using straight manifold vacuum.
But there are mitigating factors, like as mentioned with automatics, and low manifold or fluctuating manifold,vacuums.Also if your dizzy is locked, most engines won't like 55* or so between idle and 3000rpm, with anything more than a tiny bit of throttle.
Other things that play into it are compression and loading. Things like a too-low stall, or hi-way gears.
So like Aaron says"there's no right or wrong here"
I like to use the spark-port whenever possible. I only tune street cars, and the biggest was 250*
I'd like to make the following general statements;
1)Of all the automatic equipped sbm engines I have worked on, that idled at 10 inches or better with the T-Port synced up,and in gear, then the spark-port worked fine. Between 11 and 9, with mismatched stalls and gears, I have sometimes had trouble using either source.
2)With stick cars, I have always been able to make the spark-port work.