I tend to buy single effects now after mostly using multi-effects. For me its more of a personal preference though. Even though they're more expensive in the long run, I found that with multi-effects I would just get lost mucking about for ages and never get anything done. With the single pedals I find them quicker to fiddle about with and I tend to get to know them better. I like them for playing live as well as, if something is wrong, I can just take that pedal out of the loop or see immediately what the problem is rather than having to scroll through a lcd edit screen. Also, on a much more shallow note, I just prefer the look of loads of different battered pedals!
Having said that, the multi-fx pedals I used are really old now and I've heard really good things about the POD, and in the end I reckon its up to what you like!