Nothing wrong with Rocky Moutain Metro, BJC, either. I've always had good service at Denver Air Center there (the only FBO.) If you look at a map, BJC is actually a mile or so closer to the center of downtown than APA, so for me, it depends on which side of Denver I need to go to. I'm always arriving and departing from north of the metro area, so BJC actually gets me in and out quicker, and seems to have less traffic than APA.
Either one is fine, just depends on your ground logistics.
The only time going to the "big" airport, DEN, makes sense, would be if you're dropping off or picking up pax from the airlines, otherwise, the fees are expensive, and it's a long way from town.
Hope this helps, have a good trip.