Putting 2 in seems like a bigger chance of success but I did read of articles/accounts before that they also may reduce the chances of success. It really depends on embryo quality, uterus receptivity and luck.
Plus, do be mentally and physically prepared for twins or triplets if you put in two. Sounds like something fun but it also means everything is at least x2, the load you carry esp towards the end of the pregnancy, the money spent, the items to purchase, the morning sickness, risk of preterm labour. Of course, the joy is also x2 if all goes well