I've been keeping a close eye on my major connections during my time with Marshmallow. Wi-Fi, Bluetooth, LTE, and GPS can start to misbehave a week or two after an update's release. So far though, I haven't run into any problems.
GPS and AT&T's network are still holding strong. I relied on the Nexus 5's GPS to get around Chicago a few weeks ago.
I've been testing the Nexus 5 and Android 6.0 with various routers and Wi-Fi connections and I haven't encountered any problems. Connections are dependable and fast.
I've also been able to pair the device with a number of Bluetooth devices including headphones, speakers, and a Toyota Prius.
There's been a lot of discussion recently about Android Auto but it looks like those problems have been blown out of proportion.
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