Hi there,
My clinic usually try to go for day 5's but we didn't do too well with number of eggs with our cycle. Dr found 10 follicles but only retrieved 2 mature eggs. Thankfully they both fertilised but the clinic felt that since we only had two eggs we should go for a day 3 implantation. We had one embryo transferred and as you can see from my sig, we were successful. I think day 3 or 5 can be a tough decision and we were kinda lucky that we had the decision taken out of our hands. Not sure if that helped but I wanted you to know that there are success stories from day 3 transfers.
Good luck!!!