Hands down the only effect you need to use to get that arcade look is scanlines.. How many scanlines is up to personal preference in what you feel makes you remember the arcade tho.. It works best to try and calibrate it with a game you know and remember well, from an actual machine.
Usually 25% scanlines should be all that is needed.. not higher than 50% though, if I remember correctly. Also I have noticed problems with some emulators using the scanline density in reverse (so 75% is actually 25% for example) so keep that in mind if 25% looks way off compared to another emulator with the same setting.
Basically you don't want the screen to be DARK with scanlines.. you want as few possible, while obviously detecting their presence. But not so many it becomes a distraction, or you have thick black lines running across your screen.. Also with MAME you can do verticle scanlines (scanlines that run up/down instead of left/right) and I think one other additional mode.. You might find you like verticle better on all your games, so don't hesitate to try it.. I'm a purist tho, and I would only use different scanlines if I knew the game used them.
Usually 25% scanlines should be all that is needed.. not higher than 50% though, if I remember correctly. Also I have noticed problems with some emulators using the scanline density in reverse (so 75% is actually 25% for example) so keep that in mind if 25% looks way off compared to another emulator with the same setting.
Basically you don't want the screen to be DARK with scanlines.. you want as few possible, while obviously detecting their presence. But not so many it becomes a distraction, or you have thick black lines running across your screen.. Also with MAME you can do verticle scanlines (scanlines that run up/down instead of left/right) and I think one other additional mode.. You might find you like verticle better on all your games, so don't hesitate to try it.. I'm a purist tho, and I would only use different scanlines if I knew the game used them.