I use KMC 610 since years. I need to trust them chains. I wouldn't keep them for too long in any cases. They are cheap, so it's fine. 15€ every 3 months is nothing (while riding 10/+15 hours a week). Tubes cost well more than chains actually.
I recently been told that E-Kmc are actually strong(er) I might give them a try. But I won't change something that works fine since years if I still find them z610 on stock. Will see once they'll be discontinued.
I already snapped CULT (are they made by kmc ? ), shadow and Gusset half link (the worst).