Engineered flooring just means real wood flooring with a plywood backer board on the bottom. It will look the same. The most important thing is that he grade and grain matches up well with the existing flooring.

Is what you are really asking is whether you should go with prefinished flooring vs site stained and finished? As Oak & Broad notes, engineered is simply the construction of the flooring - it comes both prefinished or unfinished to be stained on site. Unless your situation dictates that you need engineered (such as putting the flooring over a concrete slab) I would use the standard hardwood and have them finished along with the existing floor to keep the colors consistent.