Since a fair amount of coolant hides in the heater core and in other coolant lines I always find a flush is better value. It ensures that 100% of the old coolant is gone, and that there is 0% chance of any weird coolant chemistry happening.
Chrissfix did a good video on youtube. my technique is slightly different.
After draining the coolant, I then run the garden hose into the bottom radiator hose and have the car run with the heater on until the discharge coming out the bottom of the radiator is clear. If your coolant system is dirty, disconnect the top radiator hose and have it discharge directly from here. Take the rad out and clean it.
Once you're confident it's all clean, you can then choose to do a 'chemical flush.' If you do repeat the previous step to ensure all the flushing agent is removed, after following the directions of the chemical flush.
Afterwards, fill with distiled water and run for a short while.
Dump that.
Refill with a coolant of your choice that meets the manufacturer specifications. (I personally like Nulon coolants here in Australia.)
guaranteed 100% clean. No old coolant. But does make a mess from running a total loss coolant system during the cleaning phase
Regards
Jordan