Do you mean what kind of receiver or what kind of software? Definitely bluetooth for the receiver so that you wouldn't have to use up a slot on the device and if you buy a different PDA. As far as the software, I use Teletype software latest and like it all though it does take some time to fully understand it. One of the best places to ask or just read up on is the website
www.gpspassion.com. There are also a lot of good retailers with links to their sites. Hope this helps you out. 0X