TightVNC is essentially dead, and based on the ancient v3 code of RealVNC. TigerVNC (the version 1.1 now in Slackware) is based on the newer v4 code of RealVNC, is much improved compared to TightVNC (speedwise in particular) but otherwise a drop-in replacement.
The same cannot be said of TigerVNC 1.2 which is a total rewrite using Fast Light Tool Kit (fltk)
for the GUI. It is not a drop-in replacement, but now that Patrick finally accepted tigervnc as a replacement for tightvnc I can work on upgrading it for the next development cycle.