There're many top players using ddkk or kkdd so it's not like you won't have fun sticking to that choice but dkkd and kddk are technically the most efficient choices.
I'm no expert by any means and probably you already know this but anyways... although there're many index players using those 2 styles, the best way is with 4 fingers. In the case of index playstyle (so just 2 fingers) you've to swap between 2 buttons with your index. The other case is using 4 fingers and it's called full-alt when it's applied properly.
Full-alt consists of always switching hand for every circle. For example, a pattern like ddkdkkd using dkkd style is played like zvxvxcz if you're using default zxcv keys, with your index fingers for k and middle fingers for d. The only flaw of this style is spinners and dk or kd streams because you're forced to singletap but overall the pros outweigh the cons.
Still, to overcome those flaws some players learned to alt in a different way: zx vc zx vc. This method is much faster and less energy-consuming than singletapping, the issue comes when you are out of dk or kd streams and need to get back to normal full-alt style, for maps with hella long streams it can cause a miss unless you practiced a lot for specific streams.
In the end it all depends on your ambitions, are you aiming for TWC finals or playing casually?
