I think it does look better to unis if you've coped with 4 A Levels and still got top grades, however if you don't think you'll be able to get AAAA or at minimum AAAB, then drop one! AABB looks worse than AAA; looks like you couldn't cope. I didn't think about dropping one of my four, cos my college don't let you take 4 ASs anyway, I had to bribe them to let me lol, so when I started A2 I didn't realise people usually dropped one, and as I wasn't struggling in any I thought there was no reson to drop one.
However, what I have found is that whilst this makes no difference throughout the year (well, except that I have to go in 5 days a week and everyone else just has 4), when it is hard is exams. I had exams every day last week and two on some days, and I've had more exams than other people. I've found this pretty stressful, and whilst it is managable and I seem to be doing okay in the exams, it is not ideal. Maybe it would be an idea to look at the proposed exam timetables for June 09 and if there's two of your subjects with exams together then drop that one, if any? It may not seem like a big deal now, but when you're in A2 and these exams have a lot of importance attatched to them, it will seem like a big deal!
But, as I have said, if you think you will be able to cope, during the exam periods specifically, then by all means go for it!