Today 10 years ago I went to Poland to buy a Phone with pre installed #Firefox OS on. The Phone was a Alcatel One, so very shitty. Two years later I installed Firefox OS on my Nexus 5 instead.
It was a very good concept, but sadly rolled out on too shitty hardware so it never caught on.
My Nexus 6 was the worst phone I've ever had. It aged like milk. It was so bad I jumped off Google phones and never went back. Getting the OnePlus 3T was like breathing fresh air again.
Edit: had the Nexus S and Nexus 4 before the 6, loved those phones... So jumping off Nexus was no small matter.
I've had android phones since the G1. The Nexus One was pretty freaking sweet, but my favorite phone of all time was either the Nexus S or the Nexus 5x. The curved screen on the S was great and it fit into the back pocket of my pants "like a glove".