Near vertical dives are effective for me. In the P38, I usually need to throttle all the way back to avoid compressibility (use dive flaps if in P38L). If you are too high to keep speeds under control even with dive flaps and chopped throttle, you can also twist rudders to add some drag, but that makes it much more difficult to aim, so I generally relax those rudders just before dropping ord.
I don't avoid vertical dives, but if all other factors are equal, I prefer to dive at 45 to 60 degrees or thereabouts. It's a lot easier to control my speed.
You also spoke of the "red cross" when referring to targeting. I think you are referring to the "Dive Bomb Sight", which is not available in most arenas. If it's available where you fly, it's a great way to aim, but as a general rule, outside of training and special situations, you won't see that red cross at all. Use it during training to get a general "feel" for the situation, but be prepared to try your aim without it in the big arenas.
-Peabody-