fit, no matter what else it has to fit
define short commutes to work abit better.... how many miles each way, will you go year round? will you be carryng stuff, will you want fenders and a rack, hilly or not hilly, etc
personally I think big bang for the buck for such a bike is in 80's Japanese bikes Brands like Nishiki, Miyata, Univega, Bridgestone, Fuji, Panasonic
if you have an idea of budget and your size, if you post your general location people will often take a peek at craigslist in your area and give you some ideas.
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Life is too short not to ride the best bike you have, as much as you can
(looking for Torpado Super light frame/fork or for Raleigh International frame fork 58cm)