Please consider that I am a novice caster. While I am a perfectionist and pay close attention to detail, I am only offering my opinion based on what I am doing and in no way am I saying anything needs to be done as I do it. Anyone who attempts casting and finds its something they will do again and again, will make their own inferences and conclusions just as I have done and make adjustments accordingly as they see fit.
So which is better...Sprue or Sprueless molds?
My guess is it depends on which one you like the least. In Theory...Sprue molds will always be the best. (My Opinion) Resin goes in one hole, pushes all the air out the back hole. Awesome. But you also have more waste. More intricate molds may prove challenging and might require more 'tweaking'. Sprueless molds allow for more delicate parts to be made and are generally easier molds to make, but the challenge is waiting till the precise moment to put the 2 halves of the mold together. There isnt much of a window for mistakes. But looks fantastic if your timing is bang on and everything goes right. Sometimes you may find you might need to fill a sprue mold a little bit first just to make sure everything is getting into all the right corners.
So there really is no better mold. Each have thier advantages/disadvantages and sometimes you need to combine the uses of both to get what you need.
My suggestion??? Make the mold sprueless first. Its silicone. You can always cut in vents after. Silicone is very forgiving. Make something small and see how you feel about sprueless. Then cut in the vents after and see which you prefer.