One year ago I bought two YN 560 IV and 6 months ago a YN 685 and YN 560 TX / YN 622C TX
I did not have any problem with them and I'm thinking to buy other couple of YN 685.
in a South American forum (I'm from Argentina) I recently read quite some users complaining about YN speedlight failing, while Godox Speedlights should have a better built in quality.
I have always known that YN products are decent but still cheap alternatives compared to Nikon/Canon speedlights but I wonder if they have recently lowered down the quality.
I doubt it. What's always happened with the cheap Chinese companies, like Yongnuo (and Godox), is that the low-low prices have to come from
somewhere. And that somewhere tends to be in QA (quality assurance) procedures to ensure consistency of built and components. Most of the units come out great, but there's a higher chance that the ones that come out not-so-great (or the bits that go in that are not-so-great) don't get caught. Because, let's face it, cheaper components probably also mean suppliers cutting costs on QA the same way.
Yongnuo/Godox are probably no better or worse than they've been in recent years (although very early on, Yongnuo really had terrible QA, as evinced by
the Strobist's 2010 review of the YN-560 Mark I--they got a lot better after that). It's just that those who get a lemon are likely to complain about it loudly on line, while those who get a good one are probably too busy going out and shooting with it to bother with posting online on messageboards. And in the end, the companies wouldn't stay in business if they were churning out more bad units than good ones.
Throw in brand-identification/fanboism and if someone, say, has decided to spend the time and money to swap their Yongnuo gear out for Godox gear, then they're more liable to say that Godox gear is simply better than Yongnuo gear to justify their expenditure, rather than better for them.
To me, Godox is a better choice if you're building a lighting system from scratch than Yongnuo not because their build quality/copy consistency is better, but because their manual-only and TTL flashes are integrated into the same radio triggering system. It'd be like being able to trigger and remote power control both your YN-685 and YN-560IVs from a YN-622-TX
with HSS on all three, and still have TTL/HSS/power control on the YN-685. You can do that on the Godox side of the fence with an X1T transmitter, a TT685 and TT600s. And they cost roughly the same as the Yongnuo equivalent gear. A TT600 is $70, a TT685 about $120, and the X1T is $50.
And you can add larger-than-speedlight strobes: the barebulb AD200, AD360II, and AD600 which all do HSS/TTL, and the plug-in studio strobes, the QTII series (which does HSS and remote power control), and the QSII and SKII series (which only do remote power control).
And Godox supports Sony and is rolling out support for micro four-thirds and Fuji X. So if you add or switch to mirrorless at some point in the future, you don't have to rebuy your lights to do OCF TTL/HSS. You just get a different X1T transmitter.
If you never plan to leave your dSLR system, and you never plan to use anything but speedlights, then the only difference with Godox is HSS with the manual-only lights. But that's still quite a bit for some folks.
See also:
Flash Havoc overview of the Godox system.