It's all really a question of how much do you want to spend. Unfortunately, cat food has gone up by a huge amount over the past few years.
I use Whiskas, occasionally some Harringtons biscuits, fresh chicken and fresh liver.
My three cats eat a minimum of ten pouches a day. Work that out and it's a lot of money!
Every cat is different. I get eight different flavours and rotate! All three cats like all the flavours, but they get bored very quickly if they aren't given a mix. They absolutely love the biscuits, but they are expensive, so I usually just sprinkle some on the Whiskas.
All three love chicken. One loves fish. Two prefer the chicken to be raw. One won't even eat the chicken if it is cooked. Same one happens to like raw liver. She also hunts for herself to supplement her diet with some natural, healthy stuff!
It's not a good idea to start them on expensive food, because it's difficult to get them off it when they get older. Anything nice you feed a cat it will expect tomorrow and demand the day after.