My Vote is deffo the Widcomm Ones.
In Order of Stability and Functionality it has to be
My Reasons behind this. I have the Latitude D820 with the 350 Card. The Dell (Toshiba Stack) though worked well for sending files and using my mobile has a phone it just couldnt not correctly use Com ports for direct phone access. I tried numerous updates and it just didnt work.
The Microsoft ones worked but I never really liked them because them lacked features found in other stacks.
I recently moved to the widcomm ones as I used to use widcomm with my old Dlink usb dongle and they worked great. Fair enough I had to fanny about getting them to work with my Dell but once working I wouldnt go back. For reference I am using the Widcomm Version 220.127.116.110 may not be the newest but it works
Oh btw hi everybody :d my first post ish saying hey all the way from the UK