I too would very much appreciate hearing opinions (and bases for those opinions) about where to try to have the cue ball strike a ball or balls in the stack (the middle balls, not the top ball or the bottom ball). Many thanks in advance.
Like Blackjack said, "it depends." I think it depends most on who you ask that question of.
If you ask Jim Rempe he'll say follow when you have a sharp angle, draw with a shallow one. Hit it only hard enough that the cue ball would go 3 rails if the pack weren't there. Rempe does like going into the top two balls.
If you ask Mike Sigel he'll say follow when you have a sharp angle, draw with a shallow one. Hit 'em hard enough to open them up but don't try to play position on the break shot. Just hit the thing and open them up. Sigel is pissed if his cue ball is parallel to his break ball, and is happy if the cue ball is one ball width closer to the side rail.
If you ask Pat Fleming he'll say the same as above, but just smash 'em open.
If you ask Tony Robles he'll show you how to get the cue ball to center table with inside draw while the opposite side top ball will pop out and go toward the side pocket so you can often get a shot on it with the cue ball rolling in that direction. In other words, Tony seems interested in playing position on the break shot.
One HOF player likes breaks from the back of the rack, and another avoids them because it sends too many balls up table and makes you go chase them
Some (I think George Fels among them) preferred to chip away at the corner balls, and steer away from the large mass of the 2 center balls.
Joe Tucker has a good book on break shots for various games. He talks about hitting the top, side, or bottom of each ball. If you know where you are going to contact the ball, you can even hit follow on a shallow angle if it suits you (my statement, not Tucker's).
Of course then there is the famous Mosconi break shot at a sharp angle. Done correctly, the balls scatter all over the lower half of the table, and the cue ball stays in the middle. "Doing it correctly" I think requires that you are Willie Mosconi. Why do virtually no professionals shoot this shot? Mystery to me. They all seem to prefer shallow breaks that they have to force. Sigel says it is because they don't know any better. :shrug: I guess it's as good a reason as any other I've heard.
Bottom line is I have yet to find any real secret that guarantees you a good break with a shot afterwords. If such a thing exists, I'd love to hear it, too. I think, for me, on a particular table, you can kind of just tell when you're hitting them too hard (balls end up clumped in funny places) or not hard enough.