Aesthetically they're all very good designs even though they're each based on a fairly simple concept. Moltres looks a bit better than the other two though so it's my favourite.
Despite that, I rarely used Moltres as I usually pick Charmander as my starter so I have no use for it. I usually use Articuno on most run throughs. I'll use Zapdos if I haven't bothered to get Raichu/Jolteon.