It depends on what you're baking. But most recipes aren't nearly as critical to amount as you think they are. If they were, the difference between a medium egg and an XL would destroy baking for everyone. But it doesn't.
My general advice is not to take too many measurements too seriously -- a rookie mistake. Everything, even in baking, is approximate. Recipes are created with pinches, handfuls and scoopfuls -- then precise equivalents are guessed. Weights are converted to approximate volumes, and vice versa; metric to avoirdupois, and so on. (Side note: avoirdupois is a "weight of peas.")
Me? I'd just use the whole egg and the heck with it. That said, both methods offered (take the half you want, or beat it and eyeball it) seem good to me. Sid and Iz are both better bakers than I'll ever be.