Just do whatever feels most comfortable and don't force yourself to play any specific way. I don't think alternating overall hurts your streaming potential because while it does prevent you from training stamina on singletaps, it allows you to play maps with higher bpm short streams, since you won't get tired out from all the "singletaps" in-between. I suspect players who alternate end up with lower sustained stream speed and higher burst stream potential than singletappers in general, but I have absolutely no basis for that conclusion beyond theorycrafting and my personal experience with alternating.