Features	VAC 3	VAC 4
Audio interface	MME	WDM
Platforms	Windows 98/ME, 2000/XP/2003	Win 5.1..10.x (Windows XP/2003/Vista/Server 2008/Win7/8/8.1/10/11) platforms, 32-bit or 64-bit.
DirectSound in Win2000/XP/2003	Emulated	Native
ASIO support	No	Yes*
Format conversion	No	Yes
Volume control	No	Yes
Work from a terminal session	Yes	No

* With an ASIO wrapper like ASIO4ALL from Michael Tippach, you can use VAC in ASIO supporting applications.

VAC3 can be better than VAC4 if both sides applications use the MME (waveIn/waveOut) audio interfaces and can be configured to use a single, common audio format. If at least one application uses DirectSound interface and/or different audio format, VAC4 is preferred.

In any case, you always can download a free trial and test both versions. VAC3 and VAC4 can coexist in the same system if you choose different installation directories and Start Menu groups. But different versions of VAC3 or VAC4 cannot coexist in the same system.