Yes, those are both ways to accomplish a flush look. It comes down to what you want out of the car and what your budget allows.
If you're simply looking for an aesthetic change and like the stock wheels (or don't want to buy new ones) then spacers are a logical way to achieve that goal. Some of the more common spacers discussed on here are from brands such as ECS Tuning, Burger Motorsports, and H&R.
Aftermarket wheels can accomplish the same thing with a different offset and/or width and that's a consideration many folks make when choosing a set.