I went for AVOs because I have had them on other cars with no issues, and they are rebuildable, and the company has always been good to communicate/deal with.
I had Protechs on my first Elan and had issues (which they have addressed by a change of design/material), and the company were not so easy to deal with (but again, it was a long time ago and others have reported far better experiences since then)
I have had GAZs on another car, but not on an Elan, and never had cause to worry about getting them worked on, so have no great comment to make.
BUT
As Jonathan says, any of them will be an improvement over 35 year old OE shocks, and even if not to exact OE specs, will seem good in use.
Go with whichever you feel happy with, whether it's because you like the colour or it is 10p cheaper - it will still be a good choice!
