15x50 or 18x50 Canon IS (1 Viewer)

Hi All, what what's the difference between the 18x50 and the 15x50?
is it hard to hold the 18x50 stable enough free hands with the IS on?
please give me the pros and cons between the 2 of them so i can decide,
thanks,

Tried the 15x and 18x a couple of years ago at a show. Three models were on display and use think the other was 12x. The 12x and 15x were equally good the 18x seemed not quite so good.

Someone else at the time was trying them and we were swapping models, we both agreed that the 15x were the best. Everything was equal between the 12x and 15x but there was the slightly better magnification on the 15's. May as well have it as everything else was the same.

The 18's were a bit bulkier and the image seemed not quite as good, also the stabilisation had to handle the 18x magnification and I suspect that 18x was just getting a bit near the limit.

The 18x50 are exactly the same size as the 15x50, so they can't be bulkier,
but i agree that the 18x are harder to hold stable, thanks for the help, i think the 18x aren't as bright as well,