For someone beginning, I don't think it is going to matter. They will both draw about the same. The biggest difference that bothers me, outside of the fact that I am just not that crazy about the looks, is that a bent stem will cause more turbulence in the draft. In the summer, you may not notice as much, but when it gets cold outside, turbulence and a cool stem is more likely to cause moisture to condense on the inner surface of the draft, causing a gurgle. Sure, sure, sure, if pushed and mot a perfectly polished straight draft will gurgle for the same reasons. But, a bent is way more likely to gurgle.
This of course can be offset by running a pipe cleaner down the draft while smoking, or drying the tobacco even more than you think necessary, and smoking slow. But, ultimately there is less room for error in a bent. Now, drying the tobacco doesn't 100% remove moisture from the smoke, as we all learned in Chemistry 101, water is the biproduct of combustion, so there's going to be moisture in the smoke regardless.
Although, most bents don't appeal to me at all visually, I do have a few that i enjoy smoking, mostly Danish bents. I just stay focused on not drawing on the smoke, and keeping it as slow as possible.