In any filmmaker's career (or impending career), the question of which to produce - a short or a feature, almost always rears its ugly and pragmatic head.
Do you step up the the challenge of pulling off a completed feature length film and possibly become the darling of the Sundance Film Festival? Or, do you create a much more modest and less glamorous short film, which is generally looked at sideways by most except those in the filmmaking world?
What's the purpose of the film? - you have to ask.
Do you want or need a vehicle with which to demonstrate your brilliance to the world? Then the answer is easy - produce a short. You can maximize your budget and retain far more production value with a shorter film. That's just some simple math there. Stretching a budget to accommodate 90 minutes of screen time is crazy unless you're an experienced filmmaker and you have a decent budget.
A smartly prepped short produced for $20K can look and feel like a studio film if you're careful.
Are you on fire to write, direct, produce, and (possibly) star (umkaaayyy) in your own film? Then you definitely need to produce a feature length film, and preferably one of at least 2 hours in duration, but don't hesitate to go for 3 hours, because nothing says "I am God's gift to cinema" - like a 2+ hour film (especially a first film). Good luck!
Is there a story you just HAVE TO tell through cinematic means? If so, you have to consider how much of a budget you have and whether or not this story can be told in a short. I'd say, let the story dictate the film length if it's about passion and find a way to finance the film, even if it takes 5 years to produce a little at a time.
Nobody has any business producing a feature (or features) until they've produced a "successful" short film. Anyone serious about filmmaking will produce shorts, and I mean *many shorts* before embarking upon the monumental task of feature length film production.
Capturing and keeping a mass audiences attention for 90 minutes is best left to professionals and YOU are not a "professional" if you've never produced a film before, let alone a film that had any significant degree of success.
©2011 Chris Santucci