Hi,
I teach on the BA Graphic Design & Illustration course at the University of Hertfordshire, so obviously my opinion is biased but hopefully i can give some general advice about applying for Illustration degrees.
1) Staff. All illustration courses have their own take on the subject. Some are more experimental, some are more fine-art based, some are more into comics, some are more commercial... so make the course you're applying for is right for you. The type of projects you're given will be dictated by the type of teaching staff, so (unless you're interested the more arty-side of things) make sure all the tutors have current industry experience (not 10/20 years ago). This means you're much more likely to finish with a portfolio that's going to get you work. Thoroughly research the credentials of the teaching staff!
2) Facilities. It's an obvious one but access to a wide range of printmaking, digital and printing facilities is vital. Make sure you check not just what kit there is but how often you're allowed access to it.
3) Contact hours. This varies massively between courses. Each institution publishes official figures regarding the amount of contact time each student gets but please double check with current students. Expect the bulk of the week to be dedicated studio time, not just one tutorial a week.
4) Quality. Rather than rely purely on reputation (which can often be out of date) judge a course on how well the current students and recent alumni are doing. If the course doesn't mention how many awards they've won recently, or if you don't recognise any of the work of its alumni - the chances are it's not performing as well as it could be.
Good luck, it's a great time to get into illustration!
Nick