I use FTW for documents, 5500/1099, and admin. I used to use Relius for everything.
To me it comes down to two things, cost and need.
On cost, FTW wins hands down.
Do you need a lot of flexibility? Relius, while sometimes tedious to work with because of all the settings and options, is a lot more detailed than FTW (and any other system I have looked at). You have to know the system pretty well to use all the bells and whistles, but if you do, you can make it do pretty much anything you want. At least this was my experience 5+ years ago.
I am happy with FTW. It does what I need it to do 99% of the time. The other 1% can be a pain and requires some creativity, but so far I haven't come across a problem I couldn't solve. Since FTW is less detailed/quirky, it is also easier to learn and use on the more basic and moderate levels.
The one thing I really miss is being able to make the reports just the way I want them, like you can with Relius. With FTW you are pretty much stuck with their formatting options (although they are working on giving us more options to customize). If you really need to change the look of the reports, you can customize it on the user end in Word, Excel or Acrobat, but you need to be creative and it helps if you have a good understanding of macros.