Used a number of different systems but for us the most effective (cost and conception) system has been the CIDR for 7 days, shot of estrumate and pull CIDR then breed off observed heats. Synchrony is usually pretty good, expect about 75% of them in within a 36hr period. The key to successful AI is accurate heat detection, there is a sufficiently big enough window for actual AI that anytime between 12 and 24hrs from onset of heat will give you good conception. The second key is days post-partum and condition of cows/heifers, this is related to nutrition and management (also prior management, cows/heifers that have had a difficult or stressful calving will be poor candidates for a synch program that seeks to bring them forward.)