Most sexually active humans try all six sex positions (yes, there really are only six when it comes to sex between a man and a woman) and as many variants as they can manage, yet we are creatures of habit and when we find something we like we tend to stick to it.
The Kama Sutra, for example, lists 64 sexual positions for intercourse between heterosexual couples with exotic names such as the milk and water embrace, or the erotic accordion, but when you strip away the fancy nomenclature, the Kama Sutra boils down to six basic positions.
They are: 1. Missionary - the male lies on top of the female who is facing him; 2. Standing - the male is standing and the female is standing with one or both legs raised; 3. Spooning - the male enters the female from behind with both partners lying on their sides; 4. Reverse cowgirl - the female sits astride the male facing away from him; 5. Cowgirl - the female sits astride the male facing him; 6. Doggy - the male enters the female from behind, either kneeling or lying on top of her.
There are pros and cons to all six of them. The "missionary" position, which is the staple of everyone's sexual diet, needs no explaining.
Standing sex tends to be quite awkward unless you have the right props. It works well if the female can sit on a bar stool, or lie back on a kitchen island, but roommates, kids and general concerns about hygiene tend to limit those opportunities.
Spooning is nice on a winter morning when your partner snuggles in behind you and, although at other times this isn't a good thing, the fact that you can't kiss might even be an advantage because you don't have to worry about morning breath.
Reverse cowgirl is a similar proposition in that you can't see your partner, but it is even more impersonal because there is barely any physical connection.
Cowgirl is more intimate because you have eye contact. However, it requires quads of steel for the cowgirl.
Lying forward from this position in a kind of reversed missionary is less strenuous, but it limits movement for your partner.
It does, however, provide decent clitoral stimulation and recent research from the Charles University in Prague has confirmed that face-to-face positions with the female on top increase the frequency of female coital orgasms.
Finally, doggy is popular with many men, but less so with women, perhaps because there is usually almost zero clitoral stimulation.
You don't mention which position is your favourite. However, as all sexual interactions have the potential to involve sensual touch, skin-to-skin contact and kissing, they should provide pleasure for you both regardless.
Although I don't see any harm in alternating between specific positions, I don't see why you can't enjoy both within one session.
Because women generally take a bit longer to become fully aroused, simultaneous orgasm is rare, but you can use that to your advantage.
Progress from foreplay to the position that your partner enjoys most and then, when you feel closer to climax, switch into your favourite position.
The interruption will lessen the excitement of your partner and help him to last longer.
When you can have it all, every time, why settle for taking turns?