Bulls generally last for 5-8 years.  Bulls can breed cows when they are 15 months old, and they reach maturity at 4 years old.  Keeping a good ratio of no more than 25 cows per bull, and periodically resting the bull from breeding will help him last longer.
There are many breeds that are popular in various locations.  If you have a cow-calf, farm-to-table, or registered cattle operation it is best to check around and determine what sells the best locally.  Angus bulls are popular due to high marbling carcass quality, adaptability, and successful market acceptance based on marketing promoted by the Angus breed associations for many years.
A calving ease bull is one who has a low birth weight and a tendency to produce calves that will be easy for the cow to birth.  If the bull has a smaller head and narrow shoulders and hips, it could be a visual sign that he would be a calving ease bull.  His pedigree or “EPDs” on his registration paper may provide additional information.