I made reservations yesterday for a campground near Denver Colorado for the last 2 weeks in July. Our first top 15 places we considered were already 100% booked, even if we split the time up between campgrounds and sites. We finally got one for that area after lots of searching.
If you know you are going, make the reservations NOW! If you wait, you'll never get into the 1st or 2nd desired site at all. You may have to settle for #15.
For us, it wasn't so much as the actual campground, as much as we had a "home base" for 9 days so we COULD explore the area.