Jon, is there any difference between your Topos and these that you know of?
Yes - tons, IMHO. It really takes a lot of work to do maps right and even then you have errors all over the place. I like to think that I put extra effort into my maps that others don't, but I'll let you determine that based on your own personal impressions of the various mapsets.
First, on the issue of the map size. The biggest difference is the coverage area. Washington 24k Topo covers only Washington, while Northwest Topos covers all of Washington, the Idaho Panhandle, about 1/3 of Oregon now, and increasing portions of BC. Here's a visual comparison of the two zoomed out to show all extent:
The size will continue to increase as I finish Oregon and work into expand into the surrounding regions.
Another difference in the two mapsets are the contour intervals. I have worked to insure that the intervals in Northwest Topos match (or exceed) what the USGS determined was the best interval for any given quad. Most mapsets out there just pick one interval for the entire mapset (it's easier). This becomes noticeable in areas where the elevation differences are not as great as in the mountains and more detail is handy. For example, here is a comparison of the area around Tokul (near Snoqualmie Falls) where Northwest Topos is using 20-foot intervals vs. Washington 24k Topo's 40-foot intervals:
Another thing that separates Northwest Topos from other mapsets out there is that I have gone to considerable efforts to obtain and incorporate land ownership/management data. This includes areas that often fall off of the radar like local and state parks, etc. For example, here is a shot of the Discovery Park area in Seattle. You can see that Northwest Topos displays the park area and details while most other mapsets just rely on national-scale areas:
Now, regarding quality. You probably noticed the lack of water around Discovery Park in Washington 24k Topo in the above comparison shot. There is something about Puget Sound in the USGS hydrology data that causes the map creation tools to hiccup. I ran into the issue when I saw that the Sound was not displaying in Northwest Topos. It took a significant amount of investigation and trial-and-error before I was able to get the Sound to display properly. Every other user-created mapset that I have seen out there has not made that effort:
Similarly, many other mapsets have completely overlooked the fact that a whole section of the Strait of Juan de Fuca and shoreline along the Olympic Peninsula east of Sequim is missing from the government data sources. I manually digitized that data using aerial imagery and topo maps.
For my last point, I'll mention that while it is easiest to just grab data from government sources and throw it quickly into a mapset, it often takes some effort to determine if everything should be displayed, or how it should be displayed. Case in point: the National Hydrology Dataset contains "extra" lines in it that are meant to show flow, but do not represent actual watercourses. These are called artificial paths and are used to indicate how streams combine in a lake, or identify river flows when the rivers themselves are large and represented as polygons rather than lines. These artificial paths are useful for some GIS analyses but serve no use on maps. I have taken the effort to remove these from my dataset and, since they are the only source for river names in the dataset (the waterbodies themselves are for whatever reason unnamed), apply the names from the artificial paths to my polygonal rivers. Other mapsets have not done this, so you see "streams" flowing through lakes and down rivers:
Oh yeah, and Northwest Topos contains all of the trails collected and integrated from Northwest Trails!
There are a bunch of other things that I have put into trying to make Northwest Topos as good as it can be, and I hope the results will speak for themselves.