The only place in China I trust for CS is Fasttech, I literally have hundreds of orders I've placed, maybe 20 issues, they've taken care of every one. Having a return address in Florida helps. They do have 2 or 3 CS reps that are horrible to communicate with, and you have to know how to deal with them.
3F maybe 25 orders so far, Customer service has been hit & miss, they ship fastest but the price is get something bad and you have to really keep after them about it. I've found initial response is good & fast, but then they tend to ignore your subsequent messages. 5 problems with them, all somewhat solved, but each time it took multiple messages to get any response, and typically was a week or two between them. Every time they apologized for missing my messages.
I did write 3F off but then decided to give them another go. I currently have an ongoing issue with them, this one will be the decision maker whether I make any future purchases with them. So far after sending them pictures of the problem they asked if they could provide the replacement in a future order. I placed an order this morning and sent them a message. It was ship in 24 so we'll see if they catch it in time, or delay the order.
Focalecig is good but slow, Doris is great to deal with on issues, and does well.
Gearbest, well they are the only one I really avoid at all cost, customer service responses have taken a month or more, shipping time is easily the worse. They pretty much refuse to get anything for replacement parts. In every case they've told me they cannot supply missing/broken parts, and always offer a partial refund. They've always taken care of the issues, but not in what I consider a satisfactory manner. roughly 30 orders from them and problems with all but 4 orders.
They do have some things you simply cannot find elsewhere, and that is the only time I've ordered from them after the initial order fiascos I've had with them.