TA - first alliance I ever had anything to do with, way back in the initial weeks!
Order of Chaos - first alliance I ever went to war against and contained some old pros such as the3rdlibra and THE SAZ.
TAA (Tauri Asgard Alliance) - all of whom were welcomed into EPA upon their disbandment.
Omega - Joined them in Quantum, struck up a good relationship with ETL there, leading to the EPA-Omega Alliance (and later the GA) once Omega started in Main.
Warlords of Briton, Bad Wolf Empire.....
The list could go on.....
But have to say that during the brief time I came back to the game (to try to resolve the break-up of the EPA) I had more dealings with Forgotten Serenity than anyone else.
And so I think Forgotten Serenity win it for me - as they are still going, with the same people, and are all good eggs!
