From a purely visual standpoint, I love the X-19. I don't have one, tried to win one on ebay a few times (only to lose to a business) but I love the look of it. That's for the JOe side. I've never been a big plane fan simply cuz they are too big for a lil guy like me to play with easily.

As for Cobra... I guess it'd be the NiteRaven. I've always like the look and love the history behind it.

Now, IF you said aircraft, it'd be a tight race 'tween NAC and X19 for GI Joe and hands down, the Mamba for Cobra. Never had a Mamba but what Outrider has shown me... Man... Totally awesome. Wish I had one.