I've tried several programs including CIDR's and Co-Synch or Ova-Synch (all with timed AI) and haven't liked any of them. In talking to a lot of people that have tried them if you get 50% conception that is probably about average. I have heard some getting up to 60-65% but more that get 35-40%.
I simply use a one shot protoglandin (Lutalyse or Estrumate) system and breed on observed heats. The cows are only handled twice, which means only splitting calves twice as opposed to handling four times in the other systems. I have gotten pretty good at catching heats and when a large group is synched they are pretty easy to find. I check twice or three times a day for about an hour each time.
I think in the end I probably spend the same amount of time with the cattle, just more of it watching them and interacting with the herd and less handling, chasing, giving needles etc. I know which i enjoy more.
In Alberta my one shot system costs me $5/head; CIDRS system would cost about $30/head and Co-Synch about $15/head.
We get 70-80% conception with a one shot system and AI'ing 12 hours after observed stand. The drawback with this system is that if the cows have cycled within the last week before the shot they won't respond so you only ever breed about 65% of the cows. However i don't mind having a few calves close in age from my clean-up bulls to see how they stack-up.
The positives to this sytem are that I spend less money on drugs, less money on semen and spend less time working the cattle and in the end I still get close to 50% of my cows AI'ed.
To be fair I have had varying success with heifers; with cows it works great and with heifers it seems to be hit and miss.