I buy some makeup when I run out of that certain thing. I buy most of my makeup at the drug store but I get certain things at mac and sephora. I have favorite brands for certain things and others I always switch up the brands; mascara:loreal, foundation:lancome, concealer:maybelline, lipstick:mac, loose powder: cover fx. other things such as blush, bronzer, eye shadow, eyeliner and lipgloss are interchangeable, though I don't always wear a full face of makeup lol.
I buy myself a foundation pot once a month, which I use maybelline dream matte mousse because it's cheap and gives an even coverage to the face and also lasts really long.
I buy the rest of my make-up whenever an item starts running out, a new mascara once every three months or so ect. I go for natural colors as every day make-up and then for nights out, I have really glittery and dark colors for special occasions and a more dramatic look.
I don't have a favorite brand, I just use what best suits my skin tone and how long it lasts.
I just get stuff that lasts for a while and doesn't make my skin break out. Cover Girl and Too Faced have really good makeup, and Sephora does too. I usually buy new makeup once or twice a year in Sephora. I only like my makeup when it looks natural, anything else makes me look like a clown. :3