I have 1 Dericam (night vision no longer comes on even though 5 of the IRs still do), 3 640x480 Foscams, 1 720p Foscam and 1 960p Foscam still in use. Had 5 640x480 Foscams until my latest purchases. Slowly but surely I'm weeding them out. I won't toss them until I can replace them...
My longest-installed (and therefore oldest remaining) cam is an Ubiquiti Aircam. It is 1280x720 with no night vision. I got it in October 2011!
It isn't really useful any more, but I leave it up anyway, like a historic building in old downtown, because it represents the past. ... Although that didn't do my old analog system any good!
I have a similar graveyard of oldies lying around here, some of which cost a small fortune in the day (PTZs). The oldest I still have in use are some Compro cube cams I now use as IP microphones since BI introduced the ability to use the audio from different cams. They've been given a new lease on life.
I still run 4 FOSCAM 18905 in areas I have yet to HIK over to new cams as I am just in transition. In my extreme weather those Foscams are bullet proof and so easy to add to any android software. The other thing I like about the bullet Foscam are the are so easy to see adn I assume crooks don't like cameras so even if I disable them I will probably leave them up.
I am still considering that Huisun mini PTZ 10x you rave about. Perhaps after they fix their firmware.
I usually keep cams for about a year, but some of these cams only lasted a few months. Hikvision, specifically 2432s have been in service the longest going over 2 years now. I see Huisun's going for as long, assuming they last.