There is no real 'best position' to get pregnant. If when making love at around the time of ovulation, penetration is achieved and ejaculation occurs then there is a good chance of getting pregnant whatever the position you are adopting.
When ejaculation occurs, the sperm are shot up inside the vagina right up to the mouth of the cervix and even higher, the sperm from there will start to move upwards aided by vaginal mucus towards the moth of the fallopian tubes where most fertilization actually takes place.
The only reason for thinking that certain positions are better than others is gravity. It is said that you cannot become pregnant if you make love standing up. This is NOT true.As I just stated, the sperm is virtually injected into place. Admittedly, whilst standing, a lot of semen will naturally flow down and flood out of the vagina... but not all of it.
It is also said that if a woman lies with her legs up for 15 minutes after making love that the chances of conception will be increased too... once again, not necessarily true.
Some women have asked me if there is something wrong because when they get up after lovemaking, even if it is the next morning, they have a flood of sperm flow out of the vagina. This is normal, but rest assured that there is still a significant amount of sperm that has already traveled right up inside towards the opening of the fallopian tubes.
I will repeat that all positions are good for getting pregnant but there are VERY slightly higher chances if you take heed of the following;In general, the best positions for getting pregnant are those where gravity won't interfere such as the missionary position or from behind... not standing up nor with the woman on top. Also, after lovemaking if you want you might try putting a cushion under your hips so as to avoid the flow of sperm out from the vagina.