That is a very subjective question. Everyone has an opinion and you can find someone that loves or hates just about every brand. My opinion is to buy the best you can afford but the very high end is usually a waste of money for most recreational divers. Brands that I like: Atomic, Apeks, Scuba Pro, Aqualung, Poseidon, higher end Oceanic and Mares. I have not used all brands but these are some I have used and like. Atomic and Apeks are probably the best breathing regs I've ever used.
My advice, shop around, find what brands can be serviced where you will be doing most of your diving. Ask other divers. Shops will try to sell you what they sell and don't always give the best advice. Buy a balanced reg. Don't buy a low end unbalanced reg from any manufacturer, you won't be happy with it in the long run. Buy a piston or diaphram reg, don't let anyone tell you one is better than the other. There are good features about both types. Don't rush into buying one. Research and ask questions once you have narrowed your search down to a few brands. Ask about the different models within each brand. A good reg will last you years. A bad one will end up hanging in the garage or on Ebay.
Good luck and ask the folks on this board and take it all with a grain of salt.