As long as you're not exceeding the rated flow rates of the 3/4" valve, it doesn't really mater much. Both valve sizes restrict the flow path as the water travels through the valve (hence the reason valves cause a pressure loss).

Based on Rainbird DV series valves (which from what I understand is the contracter version of the CP series you can purchase at places like Lowe's), the 3/4" valve is rated for flows upto 20 gpm while the 1" is rated to 40 gpm.

The only other concern would be if you're needing to minimize your pressure losses. The 1" valve will have less pressure loss than the 3/4", but based on rainbird liturature for the DV valves, the difference is only 0.5 to 1 psi difference for flow rates between 5-10 gpm.

Your water meter size will dictate how much water you can flow safely at 5 fps.
5/8 meter 12 - 14 gpm
3/4 meter 18 - 20 gpm
1" meter 38 gpm
you have calculate your total friction loss from your critical head back to you meter.Typical house here has 45psi static,with 14 gpm.I have no problems using 1" valves.If you have higher pressure you can use 3/4 valves.