If you want real fruit taste, Copper Creek is best I've found. It is uncanny how exact the flavors are. Banana and Watermelon taste like the real fruit, not some candy flavoring.
But if you have tried different vendors, the problem is probably with your tank. Just about anywhere you order from will have low resistence cartomizers (LR cartos). Boge and SmokTech and Kanger are the main manufacturers. Around 1.7 to 2.4 ohms will work best with the eGo. You have to fill them all the way, then make sure the center tube is clear.
I would try buying a box (5 cartos, around $8) next order you make. They are all I use.