If you want a dissolve that looks far far far better than any of the standard dissolves, use an optical dissolve. This dissolve treats luminance like film, big difference.
I use the SMLuminance optical dissolve for Vegas, available here.
Are your talking about transition appearance during trans from one scene to the other or for transition via a short black fade? I have the effect that I'm getting flicker shortly after the picture come from black to bright and it's only for around 1second than it's gone. Does these plugins help against this also?
It's not realy a flicker for me too, more that in the lower third or upper third of the picture a couple of lines seems to do odd things, like twinkel, directly after the fade in and it's only after a fade from black and never after a picture to picture fade. I have seen this the first time when I rendered my material as NTSC wide screen. It is not as strong when I render it as PAL wide screen. My original material is HDV 60i so I was not expecting any issues during the conversion from HDV down to NTSC but here it is :-)
Is it maybe that my fade in time (somewhere between 0.15 to 0.2 s in the timeline) is too short?
It is also less obvious on a computer TFT, I can see it much more pronounced on a CRT TV. To day, I will check it on a HD TV but I have only a downscaled DVD.