I find no difference in actual smoking based on bent vs straight (like how hard it is to draw, gurgle, etc). I prefer slight bends though purely for aesthetics, don't like full bent. Gurgle doesn't happen often for me despite rarely drying tobacco before loading it, and when it does, I just run a pipe cleaner in and that gets rid of the gurgle.
But, I do find a slight bend more comfortable even though I am a holder rather than a clencher. When holding the bowl below mouth level, the button and hole point straight in the mouth as opposed to at the roof of the mouth (like when dangling a straight). So, I guess there's that one difference to me.