I've owned far too many over the years, and resold all of them but my current 100-400mm L. The third party ones all tended to be poor by comparison, and I don't think I can even remember all of them.
I'll try to list the 300mm or longer ones from the last few years.
Canon 100-400L (2 of them, the first was not so good)
Canon 400mm f/6 L (Great lens, lack of IS and, mfd too long, and length caused me to sell it)
Canon 300mm f/4L (Another great lens, but I kept the 100-400)
Canon 600mm f/4L (Non-IS version - too much work for me to set it up and haul around)
Canon 35-350L (Very nice, but lacked IS)
Canon 28-300L (Nice lens and sharp for a superzoom. Big and heavy)
Tokina 400mm f/5.6 (The sharpest 3rd party lens I've owned, but poor construction)
Sigma 400mm f/5.6 (would not work on digital, became junk)
Tamron 200-500mm f/6.3 (Pretty bad,)
Sigma 600mm Mirror lens (2 of them) - Good for a mirror lens, but difficult to use with no IS and fixed aperture
Nikon 500mm Mirror lens (the best mirror lens I've owned)
Nikon 300mm f/2.8 (Manual focus when adapted to Canon, but nice and sharp)
Nikon 200-400mm f/4 VC I (My Nikon to Canon adapter could not adjust aperture, so I bought a cheap D300s. Nice lens)
I've also had a ton of the lesser XX-300mm lenses, some were just ok, others were bad 70-300, 75-300, 28-300, 100-300, and so on.
I buy used equipment from Craigslist if its too cheap, and get this stuff along with cameras, TC's, etc. I play with it and keep what I like. I buy new as well, when I need something specific.