This is a very interesting topic. Obviously, any good player will have a combination of both, but deciding which you would need more allows for interesting debate.
On one hand, I could have a perfect stroke, but miss every shot I take if I had issues with aiming that could come on for multiple reasons.. Excellent aiming also gives me more room for error in my stroke, allowing for a less accurate stroke to be more successful. If I get into a position of perfect aim, and miss that spot by anything under half a pocket, I can still make the ball. If my aim is a quarter pocket off to start with, that same error in stroke now causes a missed ball. Also, A good aiming system (or routine) generally infuses a good PSR into it that helps get your whole body get in line with the shot, whereas poor aim can have your whole body out of line with ths shot to start, making it that much more difficult to make the shot.
When I first really started working on and improving my stroke, I found myself frustrated that I would still miss certain shots a lot due to aiming error, and often felt that my game could be much better if my aim was more accurate. When I started using CTE (which works for me), I found that not only was I much more accurate with mildly difficult to aim shots, my confidence with hard to aim shots went way up, and I started being able to shoot these shots expecting them to go in and play position off of them with confidence. It opened up another level to my game. Oddly enough, it really improved my percentage on long straight in shots also. I always thought it was just stroke error that caused me to miss these at times, but apparently, some eye dominance issues and a lack of real good pre-shot routine (my own fault for not focusing on it) had me out of line to begin with.
On the other hand, a straight, repeatable stroke is the foundation that every other part of my game comes from. Perfect aim will do me very little if I can't make the cue ball go where it needs to from there. If my stroke error requires that I leave half the pocket for possible error, how can I shoot shots that require me to cheat the pocket with any consistency? Also, how do I every develop any real feel for position and speed play. How can I ever figure out what 1 tip of draw does with my stroke if I can't consistently hit 1 tip of english. Likewise, how do develop a good fell for speed control when I put different spins on the ball do to inaccurate stroke. I would bet that the average person that does not specifically practice stroke drills will miss where they are aiming by much more than they think they are, making all these things a reality in their game.
From personal experience, I can say that using an aiming system definitely improved my shot making percentage, and definitely increased the range of shots that I can make consistently, keeping runs going more consistently than before. On the other hand, in the past yeat I really developed a hitch in my stroke that was throwing things off on all shots requiring anything over a medium stroke. After a lot of hard work, my stroke is starting to get to a decently straight level, and I can say that the improvement now is more significant than what the aiming improvement made. My feel for spin and speed is definitely better, and run outs (while never frequent) are coming at a much higher rate than before with better position play and smoother shot making occurring at a higher level.
While I think both are necessary parts of a successful and improving game, If I had to choose one, it would be a straight stroke. Everything keys off of a straight stroke, and ones game will have the potential to reach a much higher level if they develop a straight stroke and improve from there. Without it, multiple areas of ones game will be hampered, and never develop past a certain level.
