@Leontine I completely agree it is challenging (for me at least). This question came up at my local SCBWI Illustrators monthly meeting on Saturday as we were discussing prepping portfolios for the one day conference event coming up in November.
And several of the people there could easily list a few things that they thought were their strengths or represented what they are best at illustrating.
Where as I was sitting there not able to readily decide - because my work/style etc still seems to be a bit all over the place. I came home and was looking at my website and most of my pieces shown all look completely different and it gave me a wake up call on what I need to do for my portfolio (and updates to my site once those pieces are done).
But I was still over analyzing what I would say about my own work. And that is when I thought I would pose this question to our group to see if it might helps others take a higher level look at their work as well.
So after all that is said I would say my strengths are: I am great to work with, I am best suited for children's themes and books and I love to use color!