Generally, bioware, with its low Essence cost, is the preferable option. For combat-oriented adepts, muscle toner and synaptic boosters are the biggest two, since Attribute improvement and initiative improvement are the least cost-effective things to boost with adept powers. For social adepts, tailored pheromones, a vocal range enhancer, and cosmetic mods are worth losing a point of Magic, because they stack with what you can get as an adept.
Cyberware is a lot trickier to manage, but still, getting a bit of senseware or headware can sometimes be worth it. For example, tricked-out cybereyes with a smartlink and other goodies, along with a radar sensor, for a gunslinger adept (although some prefer goggles to implants, even for mundane characters), or a commlink running empathy software and an image link for a social adept.
Overall, implants tend to be worth it for one or two Essence points, three for a few corner cases. After that, it usually reaches a point of diminishing returns.