Though both cuts have sirloin in their name, both of these popular cuts of meat come from different parts of the cow and have different characteristics. 

Sirloin steaks are from the largest muscle of the sirloin, which is a part of the short loin. The top sirloin is located at the top of the sirloin section of the cow, which is where the name comes from. Although this cut tends to be relatively lean, Top Sirloin is tender and is the best choice of cut for grilling, broiling, sauteing, or cooking on the barbeque. 

Adjacent to that is the tougher round section where the Sirloin Tip is located. The round is at the hindquarter of the cow, which is used for movement. This makes the meat leaner and less tender. Though it is less tender than Top Sirloin, Sirloin tip is the most tender of the round cuts. Because of this, the Sirloin Tip is lower in fat and a healthier option.