Flash is better in pretty much every way, especially for ADC playing bot
With ghost you do get the extra boost of chasing power but that is ALL you get. If you get CC'd or ganked at all, which you will your ghost will not save you where flash would.
If you'd like an example, lets say your pushing their tower and they have someone who is low and you want to dive. If you ghost and go for him, he will simply flash and be safe, if you have flash you have the potential to actually get an ability/attack off. Or lets say you're about to be hook by a ganking naut, his hook is about to hit you for guaranteed kill if it lands. Ghost will not save you, flash will
The main thing is not getting caught and escaping ganks, flash will save you a lot more considerably then ghost will