Quite a different mix of illustrations isn't there? For me, I find that the style of illustrations helps sets the right tone for the right scene in the right book.
For the 'Ziva and the Shetland Sheepdog' novel, I aimed the style of writing at younger readers and for Dads who wanted to write there own. Therefore, the style of illustrations had to be colourful and warm, even if the illustration was an action scene.
With the Weekend Warrior series, I needed an illustrator that appealed to the teenager audience. These illustrations were sharper, rougher and some were even borderline naughty. Luckily, the illustrator (my own brother in fact!) knew my intentions and knew not to push the limit! (Love your work Champ!)
Now, a little extra advice for you Dads who are considering using an Illustrator. 'Don't include profanity'. I don't believe in it and you certainly don't need to use it, especially as their are hundreds of ways you can portray a scene without the use of some character jumping up and down and saying the f-word over and over again.
Now, I understand that it's common in schools, worksites and even I would be a hypocrite if I said that I didn't let out a certain 'word' daily. But for me, I read books to escape the reality of the real world. That's what a book does, doesn't it? So why use it? As a writer you are creating your own world, with your own characters and your own plots. Have Aliens destroying cities or plagues wiping out nations. It's brutal, horrific, depressing but it keeps the sanity of the survivors alive.
If you go down the path of using profanity, not only will you lose the interest of the reader, but you will also be contributing to those who believe that profanity should just be accepted in everyday life.