In my opinion, the best cut of beef for kebabs is filet mignon. I also like Porterhouse and if it looks good at the butcher, ribeye. They all grill nicely and don't require a marinade to make tender. These are all great choices, but are also the most expensive cuts of meat. If you are looking for easy prep, great taste, and have no budget, go for the filet mignon. You will not be disappointed. On a side note, tenderloin/filet mignon is best served rare or medium rare. If you like your beef well done, do not waste your money on tenderloin because you are really destroying the flavor by overcooking. If you like it well done, keep reading.
If you are on a budget, sirloin tips work well if they are marinated. This will make them tender and more flavorful. Sirloin is great if you like steak well done, also. Ideally, you should start marinating sirloin the night before or in a pinch, at least a few hours before firing up your grill. You can also buy large sirloin steaks and have the butcher cut it up into cubes. It's usually free of charge for the butcher service, even at grocery stores, and will save you some prep time.
I have never had stew meat or chuck roast on a kebab. I feel it would be too tough and chewy. I can't imagine it complements the flavor of grilled vegetables much. But, to each his own!
Although you asked about best beef for kebabs, don't exclude other meats, like chicken, lamb, and even seafood. While I certainly cannot recommend cooking them on the same skewer because of varied cooking times, cooking a few different types of meat adds variety and looks great served!