What meat should be used for Bolognese?
It is absolutely worth adding ground pork or veal. I usually use a leaner ground steak and compensate with a fatty ground pork (shoulder is good) - fat = flavour.

Another tip is to take your time. Many people try and cook bolognese in half an hour, but considering ground meat is usually made with tougher cuts, you end up with tough meat and under-developed flavours. Use plenty of onions and garlic, brown your meat well, use good wine, stock, tomatoes and herbs (thyme, rosemary and bay) and gently simmer that bad boy for at least 3 hours. For ultimate flavour, cook it the day before and let the flavours marry overnight.