It can't hurt to register them both and have the secondary url forward to the main one.

I personally do not care so much for sites that use "Tube" in the name. Sure, we're all copying YouTube to one degree or another, but when I see it in the site's name, that is just too much for me. I guess I just sort of see it as saying, 'look at me, I'm another YouTube', when really, we should focus less on emulating YT and focus more on delivering a quality experience to our own niche.

Of course, that's just my personal opinion. You may very well come across a million people who would say "What do you mean you passed on using the name Gaia Tube?!?"