This is a tough call. I do really love Macross and DYRL, so those would be my pick. But for non-Macross stuff, I'd pick Project A-ko, Golden Boy, or Tenchi Muyo (the original OAV).
I would like to register my distaste for Gurren Laggan. I just don't get what there is to like about it. It's a lot like the dumb kid's cartoons I used to hate after I found anime.