I use lighter olive oils (some of the Spanish ones can be quite light & 'fruity') for cooking - they tend not to overpower the food, but I like cooking with olive oil - and more flavoursome - perhaps 'heavier' - olive oils, (often, say, Italian), or some of the better Portuguese ones, for salads. While natural yogurt has its place - and can be pretty good for for some winter type salads, (cabbage and carrot types), personally, I love an oil & lemon juice based dressing on greens. In general, I don't use olive oil 'brands' but find that good delis, or farmer's markets with links to olive oil producers, can offer good quality oils from small producers at reasonable prices.
Re cooking, it depends on preferences, what one is cooking and what one is in the mood to cook with. Sometimes, I use stainless steel, sometimes, cast iron, and sometimes - when I have plenty of time, and want to treat myself and guests, friends, family, I'll use copper.
Cheers