I find that much of the time I prefer the ratio of 18x24cm over 8x10". The holders are externally the same, so it is just a matter of deciding which to use.

On the other hand - if a 5x7" print looks to small, then so will most likely 8x10" too. I feel I need to go to 24x30cm to make a significant difference, even if it is not all that much bigger than 8x10".