If she has good technique and staying power, I don't care, but the best, most memorable blow jobs I've had I'm laying down or sitting and I'm looking down at the back of her head bobbing up and down on my dick. I can also control her head easily like that. When I'm at full erection, my dick curves upwards and position gives her maximum access without making my dick assume a more perpendicular position like when straight out on her knees. I could give a ******* about a power position thing, just make my dick feel good. I've shot some huge, powerful loads from that position!