To me, I'd say both are just as good as each other. In fact, with how I tend to do things (and the amount of ideas I spam in my notebooks) I write both for specific reasons.
For me, I'll go with this thing I tend to do. When I look at my plans, I make a note of:
what characters are involved
how many characters are involved
who it centres round
what the plot is
From there, I know whether to make it a short or a pretty long story. A story that involves less than 5 normally results in me making it a short story. However, if it focuses on less than five, but the five aren't together, I could be swayed to writing it some what longer. At the end of the day, it really depends on what you have in front of you.
On the other hand, I tend to write longer stories more often and, like most people, do struggle with keeping it all updated. However, I always come across moments where connections between my stories are sort of left hanging. This isn't intentional; it just happens. This is normally when short stories come into play (when I'm not doing them for contests and other stuff.) If I do a short story to tie up the ends of one story and lead it on to the start of the next, my mind often tells me that 'it's not as important since it's only a short.' But I know that isn't true since I find that events that happen in the shorts aren't spread out between chapters. This means that I feel like I can write as much detail about that event than I could in longer stories. (Unfortunately, I'm one of those that has to spread longer scenes across chapters for the sheer case of my mind won't allow it any other way in a long story.) Because of that, in my opinion, it allows me to take the reader along with me, rather than leaving them waiting mid-way through. It's good to do, but not every time.
Well, that's my opinion on the whole thing. As I said, I use each in a nice balance and wouldn't write any other way. ^^