I did a little experiment this past summer up in Northern Ontario.
For those who don't know, out in the bush in Northern Ontario the bugs - mosquitoes and black flies are insane.

For the experiment I tried:
Deep Woods Off
Johnson's Baby Creamy Oil with Aloe and Vit E.
Oil of Oregano from Natural Factors(small bottle with dropper - NOT the concentrated stuff)

Oil of Oregano worked the best.
Deep Woods Off was the worst. It only kept the bugs off me for about 45 seconds after it was applied.