It isn't just the type of flavoring but its also the brand or manufacturer. TFA flavors for example often require a higher flavor percentage than say ecig express' brand b/c ecig express makes a more concentrated flavor. Other brands will also require more or less.
They do somewhat vary by type also. Fruit flavorings to me require the most flavoring, followed by coffee flavors, then dessert flavors and finally, tobacco flavors you would use a very small flavor percentage.
In general, a good starting point for any flavor is going to be simple to google that flavor and brand to see where others start. If you say google Flavour Art Peach, you'll find some percentages here that people recommend. If you still can't find it, ask on the DIY board. It's a continuing knowledge base and we all benefit.