I have had very good experience too with JLCPCB, I think i'm at about my 50th order or so, a mix of 2 and 4 layer board (from 10 pcs prototype to 3000 pcs at most).
All have been at a very good quality (smallest geometry is for 0.8mm pitch BGA).
I only have one thing that I think could be (much) better! I have tried explaining them that their "ship with already ongoing order" is not working too well. If it is a language barrier or not I don't know, but I have a hard time getting them to understand (or maybe they wont ?) what this is about...
PCBWAY etc all have this feature too and it works perfectly, when adding a new order you can select if you want that shipped with one of your "already in production" orders. You are warned that your complete shipment will be delayed until the order that is finished last, is ready. Which is perfectly fine.
But, JLCPCB.... Well, they have the same feature, and it kinda works.... But, only if you send an order that is accepted immediately for payment. If it is put on hold for some engineer to look at it, once it clears and you are ready to pay for it, you are no longer getting the option for bundling it together with the "already in production" order.
With the amount of projects/PCBs I order from them, this would have allowed me to save substantially on shipping. I often have projects coming in a row, wanting to send a new design while something is in production with them.
Other than that, all is nice and dandy