I always wanted to go to day 5 as I believed that if I got to day 5 I was half way there. I only ever did 3 day transfers with the first clinic I worked with, I did get 1 baby which started off as 3 but then when I went to a clinic that did 5 day transfers I was lucky first time with twins. My clinic froze most embryos on day 3 and only grew 3 to blast - 3 made it to blast BTW.
I have heard that the success rates are the same on day 2, day 3 or day 5 and live birth rate also. One clinic I work with does mainly day 2 transfers but will go to blast if you insist although the day 2 transfer is a european thing mainly.
Personally I would freeze half on day 3 and take half to blast as the pp said - obviously assuming you have enough good quality embryos.