I just started Geocaching today and I used BCN and CacheMate. I can tell you that it would be nice to have the "Log Found" feature directly in BCN. I haven't had the pleasure of finding a Travel Bug yet, so I can't comment on that functionality.
However, with CM you can log your find, then export the GPX file with that information in it and then either import that into GSAK, or use the Geocaching Express Logger
http://boulter.com/geocaching/logger/ to log your find back on the Geocaching.com website. Mainly you would just need to support the Cachemate extensions to the GPX xml schema.
Also, using both programs, it was easy for me to use the GPS features of BCN, but then have the details of the cache I was looking for up in CM and switch back and forth. To load the cache details in BCN it is a modal window that I have to close to go back to the map, and then find and edit/open again to look at the details. If that could just be a tab like Map/List/Data, etc on the bottom it would be great.
I haven't purchased yet, I probaly will, I'm just trying to figure out if I want to pay for maps or use the terraserver ones, I'm heavily leaning toward BCN at this point though. I love the tracking feature.