With new chassis, pretty much any brand that has a good reputation and offers dealer support will be fine - especially for beginning racers. If you pick a brand that is popular at your track then it will be easier to get answers to your questions that actually help you. After you gain enough experience to figure out what you like / how to adjust you might try a brand that isn't as highly popular at your track, under the guise of it's easier to beat people if you have different stuff than they have... but you also have to be willing to go through a tougher learning curve.
With used chassis, there are pluses and minuses. They will be cheaper, and it is possible to get a bunch of setup information from the seller. But if they were raced a lot they might have metal fatigue or have taken a set that will hamper handling, and they might have hidden wreck damage. It can be hard to discover this, even if you have experience. You also are better off to stick to designs that aren't more than seven or eight years old since chassis design technology moves rather quickly. Some people have enough talent or experience to make almost any old kart fast, but if you are a beginner you'll have less frustration and are less likely to learn bad driving habits on a newer design.
Factor in what you expect to get out of racing. If you are willing to start out knowing that you're unlikely to win right away anyway, and want to reign in costs while you learn, a decent used popular brand kart will be fine. If you need to be able to run up front or you'll get frustrated and mad, better buy a new popular brand kart (as well as find experienced help).