Worse:
A small village outside Pingguo, Guangxi.  We visited it (a group of Ex-Pats) with a small van.  One of the elders called the Police complaining they were invaded by foreigners, Police came and eventually we were released, apologies given.  But it was scary for a while.
Best:
Buddist Area and Temple near Sanya, Hainan Island.  You have to pay to get in, but scenery is wonderful, Temples are great, and food served for lunch, even vegetarian, was excellent and planiful.

Forbidden City was, for me, nothing more than an overcrowded area that looked identical each time I went to the next section. Keep your money...nothing to see there.

The Shanghai Expo was one of the worst tourist attractions I've ever been to. I was on a tour in China, and we had to go there, we didn't have a choice. It was during the National holiday in October, so it was extremely crowded, and not worth it in my opinion.

The best? Nothing really stands out, but I haven't traveled that much in China yet. Give me a while, I'll probably have something within a few months.

The Ming Tombs, Man what a Freakshow that is. Hour wasted shuffling around these narrow halls that are underground and have unseen tombs behind some unseen glass stacked with unknown amounts of hard cash given by the minions over unknown number of years.

Studipest thing i have ever seen. On the plus side the park around the tombs is very nice and we are rolled some green under a tree there to make the pointless shuffling..... well pointless with a buzz.

I went to this large indoor water park near Shenyang. Some people took me there thinking I would be impressed. I have lived my whole life by the ocean having been born and raised near the beach on the beautiful coastline north of Wollongong in Australia. To say I was underwhelmed is an huge understatement. It was crowded, the water was disgustingly dirty and the highlight for me was probably having my first look at swimming attire Chinese style. There was supposed to be a sort of wave pool. Believe me I make bigger waves when I fart in the bath.

Hands down the worst would be any zoo here.  If you have any feeling for animals, besides they're yummy, it'll make you cry.

Best.... Just get a car and drive up to the Tibetian Plateau.

The best one, undoubtedly, are Luoyang's Longmen Caves with intagliated buddhas. Really unforgettable! 
And the worst is, probably, the Ming Tombs - nothing to do or explore at all, even if you are keen on learning Chinese History as I am!  

The worst the silk markets...The best would be someplace either in Macau or Hong Kong...

Bruce Lee's grand fathers home where it is rumored that Bruce spent 1 night when he was very, very young.  150RMB a person & I had 9 people with me.  :(

The Best: Huashan outside of Xian was a discovery for me. Everywhere I turned at the top of the mountains just took my breadth away. I would want to go back some day and do a proper exploration of the entire park.

The Worst: The Silk Market in Beijing is a total waste of time.

The worst: Any one of the half-dozen revolutionary museums I've been to. I love history, but the displays were not well planned, nor were the translations sensible.

The best: Zhang Jia Jie in northwestern Hunan province. A world heritage site, it was one increadible mountain vista after another for three days. The quintessential Chinese landscape that one sees portrayed in ancient paintings.