I'm already partially "bionic", I have a titanium replacement hip joint.
But for starters, if cost was an issue, I would go with bionic legs, hips and spine. That's the foundation for body strength right there. I wouldnt want bionic arms if every time I went to chuck something heavy I'd be throwing out my back. With bionic legs/hips/spine, I would be able to run faster, go longer without resting, and have the physical foundation for greater feats of strength. If I could go all out, I would love to be 90%+ bionic, think a Warhammer 40K Mechanicum Magos.