I have used nearly all of the above (and the Ariadne II mentioned later) and found the Ariadne was pretty much the easiest to install and deal with. While it otherwise seemed pretty good, I ran into some weirdness with the x-surf and other software (but it's been too long to remember what it was) so sold it.
The A2065 (or was it the hydra?) used coax, not rj45, so it required a terminator and an older hub that still had a coax port, but otherwise worked fine (but if you find one, buy the hub and terminator with it if you can).
A couple not mentioned already are the variations on PCMCIA ethernet (there were at least two on the market at one time, one I got from National Amiga in canada, can't remember on the other) and, the DKB A2000 68060 accel. has ethernet built into it, if you are lucky enough to find one still out there (definitely among the rarer, yet coolest hardware out there for the Amiga ever made).
Finally, I would imagine now that you might use one of the various still-avail. USB cards as an ethernet alternative too? I've done that route on occasion with PCs, why not Amigas?
good luck!
amigau
http://www.amigau.com
