I use both MS Streets & Trips, the most recent version. Now that Microsoft decided to abandon it, if you can still buy one then get it as you will not be disappointed.
MS S&T is installed on Windows 7 Ultimate. This version also has a virtual machine. BaseCamp is installed on the VM with another copy of Windows 7 Ultimate. So for mapping, both OS's are running on a single machine.
Planning a trip on MS S&T is the most easiest, in my opinion.
I could export it into .gpx file, but it has some quirks ... will explain a bit later
I have two 24" hi-res monitors, and run MS S&T on one monitor and BaseCamp on the other monitor. I roughly remap it in BaseCamp. Once done, I then zoom-in to check where I have placed markers. Like someone said, make sure it's not on the opposite side of the divided highway.
Finally, I then export my trips out of BaseCamp straight onto the Garmin piece.
I have noticed that when you create a trip in S&T and decide to export it into .gpx file. It exports without a problem. The problem arises when you try to import the .gpx into BaseCamp. It will give you error ... some like bad file or some sort. I figured out, if my memory serves well that there is a date/time stamp issue. Once you edit the file in a text editor and save it back, BaseCamp can then import the file.
, some times S&T will calculate the route to your liking, i.e. you may not need to put markers that often, but when you import that into BaseCamp, BaseCamp may recalculate it differently based on it's own algorithm. In this case, you would have to go and fix the routing. So, first it's the Microsoft issue when exporting the file (it could also be that Garmin doesn't like Microsoft's way of doing things), second, recalculation algorithms are different in both systems.
I have not proof read this long note, so if there are grammatical or spelling errors, try to figure out yourself what the sentence means.