Is it better to request a recommendation letter in person after class or by email? I am planning to apply for a PhD program and would like to request a letter of recommendation from a professor. However, I am quite hesitant about which way is better for me to make the initial request: asking the professor during the break of the class or just sending him an email?
My recommendation is definitely in person "after class". There are several reasons to do so. First, it is personal and you can iron out any details there and then. Second, the person you approach will have a face to go with any future e-mail conversations. Third, it is less likely a person will dismiss you in a direct approach than in an (impersonal) e-mail approach.

There are of course ways in which you can blow your hopes with a personal approach as well. Just be brief and to the point, try to be professional about it. If the person appears not to have time, ask if you can meet during an office hour or if an E-mail would be better. After all, you have just presented yourself and is now "a face".

There is of course nothing wrong with just sending an E-mail but I know from personal experience that I sometimes get mails from students who apparently have attended my classes but made no impression so I ask myself, who the ...  is this? Not a great basis for a letter of recommendation. I personally also think that a personal approach shows more initiative and drive. All this is of course from the perspective that you actually can meet with the person without engaging in long distance travelling etc.