In my opinion, Madvapes is the Home Depot of vaping vendors. For mod and kit builders, they are unbeatable. Shipping cost is low, customer service is generally prompt and good. Sales/coupon codes are infrequent, but their regular prices are so low that it's as if everything is on sale all the time. A big thumbs-up.
Their China E-Liquids line of pre-mix Dekang tobacco flavor juices in 50ml bottles is terrific. Their other Dekang line, called Custom China E-Liquids, varies in quality, or so the customer reviews suggest.
Madvapes' Top Vapor USA juices (mostly non-tobacco flavors) are---for me---hit or miss. Sometimes very good, other times not so hot. Over the past nine months, I've bought 20 bottles of Top Vapor juice, and it's running about 2/3 good, 1/3 meh. Of the ones I don't like so much, they're not terrible, just not as good as other vendors' offerings in the same flavors---not perfumey, as I recall, but occasionally marked by a chemical aftertaste.
Still, no gripes here.