So with calculator and pad in hand, I hopped on over to the USDA nutrient data base and pieced together on-the-go versions of the two sandwiches. Neither was overstuffed. The PB & J had two tablespoons of peanut butter and one tablespoon of jelly. The turkey and avo had a 1/4 cup avocado, about 2 1/2 ounces turkey (75 grams) and a dash of mayonnaise (1/3 tablespoon).
Not too surprisingly, the two sandwiches stack up pretty well (see table below). Calories, fat, and sodium are basically the same. Where they mainly differ is in the protein and carbs. The turkey and avo has more protein and fewer carbs than the PB & J. The PB & J has more carbs and less protein.
So if you're looking for a decent amount of protein with a great carb boost, the PB & J is a good choice. If you want a bolus of protein with some pretty good carbs, turkey and avo may be the thing. Clearly, one of the most important factors is simply which sandwich sounds good to you at the time, and whichever it is it'll have some good fuel to get you to the finishing line.
(Creative Commons photo by iirraa)