I think with a five day blast it gives you more chance to choose the most promising looking one. There seems to be a drop off between day 3 and 5. You need a few good ones to chose from though. I only had one egg so no work for the embryologist at all to chose from, so they stuck it back in on day 2! Better in that out, apparently. It'll be a miracle if it takes.
Thanks for the new thread @Lemongrass1.
Good luck those with upcoming transfers.