Line out of the amp if it's available, speaker out with a d/i with that type of input option. 'Stewart ADB-1 for example. (split' it with the speaker -don't do d/i only unless the amp's designed to.
Try it and see, as long as you don't hook up a speaker out you can try almost anything until you find what works best 4 U. I tend to use modelers or multi effects for recording over actual amps unless I need feedback.