I build both, and like building both, they each offer different challenges. Replicas require research, and fiddling to get it to not look like a clipped mess. However, custom craft can use stock part profiles, heights, and wing shapes, which makes it quite a bit easier than replicas, after all, custom crafts don't need to work one specific way. As to creativity, I feel like there's just as much creativity in trying to get stock parts to look like a IRL craft, as in building something from scratch.