Well, my personal preferences would be: 1) doggy style, and 2) missionary
I LOVE fucking my wife from behind while she's on all-fours. I enjoy pushing her head down to the mattress, holding her hips, and watching my cock go in-and-out of her pussy. Of course, I'm also thinking about "accidentally' slipping my cock up her ass which she never allows - but, hey, a guy can fantasize, right. I'm not a complete pig, however, so in doggy I do reach around and massage her clit. And, for whatever reason, I find that her clit seems to get larger in this position.
My second favorite and most-often position is missionary. I enjoy holding my wife in my arms, touching her face with my hands, kissing her ears, neck, lips all the while being inside of her. She really squeezes and relaxes her pussy in this position which I LOVE. I don't know if she gets much out of that but it feels damn great to me. In this position, she also reaches underneath her leg and plays with my balls which is heavenly to me while we're fucking. Within the last year, my wife has been positioning her legs in a more "open" position which seems to allow me to get the deepest inside of her. I'm just average in size but OMG, the feeling of her accepting me as deeply as I can go is fantastic. Of course, from missionary I'll sometimes rise to my knees, grab her legs, and put them on my shoulders. I love the sight of my cock going into her pussy and her tits jiggling with each stroke. This way, I can also play with her nipples.