by DreamcastPast » Thu Jul 04, 2013 4:54 pm
Buying a VGA box made for the Dreamcast will give you the higher 480P signal, rather than the standard 480i signal used by the scart output etc. I'd personally only buy a VGA box to make sure I was getting a 480P signal. If you want to try a boxless cable that supposedly gives you the same performance of a VGA box then you'd need to make sure that they output a signal of 480P before buying!!
As for scanline generators or line doublers, it depends what you want to play... they are mainly used for older arcade boards that out put 240, scanlines are added every other line to bring the res up to 480P... but games like Shenmue are already pushing out 480P with the VGA box. If you were using your DC for 2D sprite based games like shmups and Street Fighter 2 type games then they can look quite nice with scanlines as they are output at 240, but generally avoid if you are playing '3D' graphic games like Shenmue, Crazy Taxi etc etc...
For more info on scanline generators/line doublers look at faginrs500's youtube channel...
And one last thing to consider... upscalers and scanline generators are processing the image, this takes time. Some people have been experiencing slight input lag when using these devices, not much, around 1 frame per second (the DC runs at around 30 frames per second), some people notice it, some don't, but something to consider.
My preferred set up: For sharpest picture and quickest performance keep it simple. As I said before: DC + VGA Box + CRT computer monitor.