The cheap hdmi converters are about as bad as the built in up-scaling of modern TVs. Manufacturers have no interest in supporting analog video anymore, so the only do the bare minimum. Your best bet is to get a wiiU and use that. Failing that, get an OLD tv. I had a Philips plasma that gave an excellent picture from analog sources, the up-scaling was nearest-neighbour so it retained the pixel clarity and my Wii though a component cable was absolutely perfect.
Unless you want to spend $200 or more on an up-scaler, then you're stuck with a poor picture, we all are.