Ed,
LaBVIEW can use COM/ActiveX components, C dll's and C++ dll provided that the c++ dll has direct function calls(you can always use a wrapper dll to call functions inside a class)
As far as what labVIEW users prefer, this is kind of a difficult question to answer since it is mostly dependant on the users knowledge of each of those components.here are a few links that may interests you.
http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/5401be584fbaeece862567c2006d36c7?OpenDocument
http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/7f41004ee990d4da86256a9d0064d522?OpenDocument
http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/3a1f4b7cbc68b636862567cc004d5cca?OpenDocument
and more gener
ally
http://zone.ni.com/devzone/devzone.nsf/webcategories/4161F118BF99CCE686256AB7006A68EB?opendocument&node=DZ53001_US
Regards,
Cyril Bouton
Applications Engineer
National Instruments
Cyril Bouton
Active LabVIEW Developper