At some point in time I became paranoid of using VST3 plugs as well as VST2 plugs in a project.  Maybe it was a situation where I used one of each for the same plug - can't remember, but there was crashing and gnashing of teeth.  Anyway, I would love to hear a few comments on this.  Cool to do?  The reason I ask is I am thinking of eliminating all but one flavor, specifically on Melodyne, as another thread talks about that as a remedial action against Melodyne misbehaving.
 
So the question here is: in general, is it OK to mix the two kinds of plugs?  Then a follow-on question of whether having two of the same plug, one in VST3 and another in VST2 in the same project, a bad idea?
 
Cheers,
Steve

I mix DirectX, VST2, and VST3 with impunity. Live dangerously! I hardly ever get crashes so I don't think it's a problem, but then again, I use only Cakewalk or trusted plug-ins. I'm not a fan of downloading floozy plug-ins from the internet, if you know what I mean...
 
If you're freaked out about it, choose one format as your primary format. If you use another format,  render the track with the effect to do your mix, delete the effect, then archive the track just in case you want to re-visit the original someday.
 
 
 
 

AFAIK, only Waves plug-ins cannot be mixed. Mixing Waves VST2 and VST3 plug-ins can crash a DAW.