* Geeksphone Revolution - the most powerful phone but its running on a x86 architecture and the port is done by Geeksphone, even though they released three new updates already there are still bugs.
* Alcatel One Touch Fire - great phone and is unlockable with some exploits. Better than ZTE Open IMHO.
* LG Fireweb - better specs than the ZTE Open and Alcated OT Fire but its as locked as fort knox regarding the bootloader. You will not be able to flash your own device. If that is not a problem then its a great device.
* Geeksphone Peak - the second highest spec. Larger resolution than most retail devices and CPU but I think the battery drains too fast, I'd rather use Revolution.
* Geeksphone Keon - The standard developer phone for Firefox OS. Wonderful tiny device, the screen sux but the specs are better than the ZTE, Alcatel and LG.
My recommendation is to wait for the flame:
https://developer.mozilla.org/en-US/Firefox_OS/Developer_pho...
I have all the phones above. My daily driver is the Geeksphone Revolution and I've used the Fireweb and Alcatel daily before that. The Peak would drain too fast.
Disclaimer: I am a Mozilla Rep and member of the Brazilian Firefox OS Launch Team. If you're interested in developing apps for Firefox OS I've authored a free and open book about it available at:
http://leanpub.com/quickguidefirefoxosdevelopment/
I will hang around this topic if anyone has questions.
;-)