When using a TV, I think probably your best results for full screen with most games will be to enable hardware stretch (assuming your video card supports it) and use the "RGB sharp" filter. In the command line version of MAME, check the documentation in the Docs folder to see how to set the filter in the mame.ini file. In MAME32, which probably isn't the best option available for TV display, you can enable these options right from the gui.