Which 500 mm camera lens is better and why - refractive or reflective?

I have a Nikon and have bought a few Tamron lenses and have no complaints. Here is a discontinued zoom model with good reviews that will save you almost $1,500.00

Refractive lens will give you sharper brighter, images every time. Reflective lens don’t allow for any control over aperture and will often have a smaller aperture than a standard prime lens. You’ll also have to focus manually (but given that you’ve been using FD lenses til recently that’s probably not a problem). The build quality particularly on canon telefocus primes also means they’ll probably last a lot longer than a third party mirror lens. Having said that the down side is that big canon primes are expensive, small car expensive, a 500mm f4 will set you back £6k and an f2.8 will probably be twice that. You can go second hand but these things tend to hold their value amazingly well. Mirror lenses on the other hand are cheap, my local camera shop stocks a 500mm mirror lens for just over £100.

If you are intending to use the lens for professional shots then its a no brainer refractive primes are the only option. If on the other hand you hobbyist then a 500mm mirror lens is probably a much more sensible. You can have a ton of fun with it, it’ll be easier to carry about because it wont have 5kg of glass in it and you won’t care if you damage it in the great outdoors because they’re as cheap as chips. Another option is (like @Cruiser says) it to go with a zoom. There are quite a few third party zooms that cover 500mm, it’ll give you more options, and you’ll need less lenses and will be significantly cheaper than a prime. OK it’ll have a smaller aperture and probably won’t be fixed but it’ll still probably be brighter than a mirror lens.