Both are very difficult, but building is tougher. Maintaining just takes more work, not harder, just more.
I think it boils down to your location. If you are in an area with a strong soccer tradition, strong clubs, and good parental support, you'll attract good coaches and will be able to maintain a quality program. You may not win state every year, but you will consistently be among the top teams. Look at any division and I bet with a few exceptions the top 15 this year are mostly the same as five years ago.
A few years ago I ran a couple marathons. Getting in shape, losing weight, changing my diet, and accumulating the miles was very difficult. Maintaining was easy compared to getting in shape.