For me, personally, LITFL is their epic song. It's the one I can remember being blown away by as a young kid. The opening guitar riff got me hooked, and I've stayed hooked on that song. With HC, I loved the beginning, but I'd be sad when Don sang "but you can never leave" because I'd think "crap.. here come the guitars" . It wasn't until I was almost a teenager that I began to love and enjoy the guitar part of HC.
I think that Felder made them a bit better, but it was adding Joe Walsh that really took things from successful to mega - successful. Joe not only brought talents as a guitarist, but as a songwriter and vocalist. He also already had an established career and fanbase. His fun, kind of crazy onstage persona, I'm sure also helped bring the crowds. Felder was a no-name struggling musician playing for Crosby and Nash. He brought talent as a guitarist and maybe as a songwriter, but certainly nothing like the talents and "perks" Joe Walsh brought.
As for songwriting and who gets credit, I'm not sure. Going back to LITFL, Joe gets a songwriting credit for the riff, even though it was Glenn who saw the potential for it to be part of a huge song. In fact,isn't Joe's name listed first on the credits?(Someone correct me if I'm wrong). I've always been a bit iffy on who gets credit for helping to write a song.
I've only been a mega-fan for about 3 months now, and I'm already tired of reading about "Don Felder and his amazing song, Hotel California, which he pratically wrote by himself". I'm glad that I didn't read his book prior to watching the documentary or checking into the band more. I might be on the other side of the debate.