My favorite position for just me and my wife is cowgirl - I love having her on top, so I can watch her big tits jiggle and bounce, while she rides on my hard cock. The sight of my cock penetrating her, sliding in and out of her wet pussy is so hot.
My favorite position for watching her include what's usually called "fuck licking" - me on the bottom, her on top, in a 69-position, so I can watch her lover's cock penetrate her, and lick her clit, or if I am purely watching, and not participating, I like to set at the foot of the bed, with her in a reverse cow girl position, riding her lover's cock. We can make eye contact, occasionally kiss, and I can see her being penetrated.