for a serve adn volly, it is good to have a lot of pace. that really tends to mess people up. if you arent too fast,a nd you leave a serve within reach, you are basically in no mans land by the time the return comes back, so there sis where spin si good, it gives you time. in general though, a good placed down the T first serve to both sides with a good amount of pace, maybe 90% as hard as you can hit it, is a solid play, and will set up for a bunch of easy put aways. most importantly, keep mixing it up, no matter how good your serve is, your opponent will basically start sitting on your pacea dns sending it back at you harder than it came to him. so the answer to your question is hit both. use both together, seperatly, whatever gives the guy on the other side of the net trouble.