What forms of maledict affect mobs hitting you the most? -str, -dex?

I can see -str lowering their hit roll, making your -AC more significant increasing miss chances and your chance to block with a piece of armor..

A follow up to that, the Stat Analysis says STR starts affecting hit/dam at 19. Can you get -hit/-dam if your strength drops to, say, below 10 or some other arbitrary number?

Thanks.