One of my favorite hikes to do, if you are at the base of the mountain by the parking lot if you go left its paved all the up and it's way steeper and it zigzags back and forth up the mountain. If you go right it's less steep but it is unpaved. If you want to get an over look of Prescott and climb to the top, it may be a bit challenging for some to get to the top so it is not recommended. But if you plan on going to the top it is only closed from February 1st - July 15th.
Starting on the left is much more of an incline. The trail is well established; much of it is paved. There's also a lot of information on the surroundings throughout the trail. Every once in s while you get s good view of the landscape. If you're used to the altitude I would rate this as easy.
We hiked this trail with our two sons, ages 9 and 11. The original incline was a little rough on our 9 year old, but he eventually got into it and enjoyed the scenery, trees, and views (with a few stops along the way to rest up). By the end, he was happy to have completed the loop. We would definitely do it again!
Approximately 20 years ago I climbed all the way to the top of Thumb Butte a couple of times. In August of 2015 My wife and I took our visiting granddaughter on the Thumb Butte trail, expecting to go all the way to the top. The way to the very top was no longer there. What happened? Or is there still some way up? Any comments?