Sometimes I cringe when I see even a wisp of a carrot in a spring roll. It's just a reflex, because I believe, in principle, there's nothing wrong with having carrots in a spring roll. But if I had things my way, I would definitely not put carrots in spring rolls. I would stick to the classics, like napa cabbage or really any cabbage or leafy green that can be made juicy and tender.
Now why do I dislike carrots in my spring rolls? For starters, the carrots are usually not precooked so they remain as raw slivers inside an otherwise cooked filling. But somebody must like the pairing since so many of the spring rolls I have bitten into in the States contain carrots.
In China spring rolls tend to be quite small and made with very thin wrappers. Deep-fried, there is such a terrific contrast between the crispy shell and the tender, carrot-free interior. The filling is so soft and full of flavorful cabbage-y liquid, thickened with cornstarch for that signature "velvety" sheen. In addition to cabbage, you might find little slivers of stir-fried pork or mushroom or bean sprouts.
In Shanghai spring rolls are made with napa cabbage, cooked down for hours until it becomes a thick vegetable puree. It may take a while to cook the cabbage but it's a simple recipe with few ingredients. Instead of being stir-fried, thinly sliced pork is simmered along with the cabbage. It's almost as if a savory cabbage soup is trapped inside the crispy shell.
And none of that "duck sauce" or "orange sauce" that often accompanies spring rolls in the States. Instead, only a little bowl of vinegar to dip. It might just change your whole outlook on spring rolls.