For 480i content the Framemeister is better in all ways except for input lag where OSSC is the clear winner. For 480p content the OSSC only transcodes/converts into digital (well, unless you use the 480px2 mode but that’s very jaggy and doesn’t work on all TVs).
Putting the VP50 up against the Framemeister is a much harder question to answer. I’d go have a look at http://retrogaming.hazard-city.de/
If you’re after smoothing out jagged edges or “refining” the picture on 3D games you might need to look at emulation, there’s only so much you can do with upscaling.