I had an attached 30a cord on our first trailer and now have a detachable 50a cord on the new one. There are pros and cons to each in my mind:
1. Detachable was quicker to deploy and pack up. There is nowhere to easily store the detachable cable on the side of the TT where the power connector is, so I lug the heavy 50a cable to the other side, where it lives in a plastic bin on the bathroom floor during travel/storage.
2. The attached cord decided to feed itself out onto the highway once. By the time I was made aware of it, it was half destroyed. I fixed that problem, but obviously it wouldn't happen with a detachable.
3. It would have been impossible to get to the storage cabinet in the event that the cable ever needed total replacement. It was behind the bed in the rear of the TT, and I saw no way to access it short of dismantling walls. That being said, I have no evidence that anything crawling into that compartment would have found its way into the house proper.
So I'm basically on the fence as to which I prefer. I see both sides of the argument. Perhaps I might change my mind after lugging the cable 'round the trailer a few dozen more times. :)