Steam works fine and I have never had to their CS, download speeds are good and they have regular offers.
I had some issues in the past with Origin but after contacting their CS and sometimes making a phone call they have always resolved my problems in the end. Download speeds are good and they have regular offers.
I have had to contact Uplay on 2 occasions and they were completely useless on both occasions. Useless Customer Service, overpriced games and buggy releases for pretty much makes them the worst of the worst for me.
I'll only buy a Ubisoft game if its on offer via a third party site nowadays, its a shame because they make some good games but being a 4K games I need games to actually work to enjoy them.
Just my opinion, if anyone has anything good to say about Uplay I'd be interested to hear it.