Best type of bike for Chinese conditions.

China is obviously a huge country, so conditions will obviously vary across the country.

Northern and western China (north of Shanghai) can be very dry in the summer and Autumn, this means that thorns are a serious problem so bring tire protection if you can, and tires good for hard-pack conditions as sometimes tire choices in China can be frustrating. In southern China conditions are much wetter and mud specific tires are a good choice.

Hardtail XC bikes are mostly the best bikes for off road use, as mostly there are no real trails as such, although around some bigger cities there are mountain bike specific tracks, but there are millions of kilometers of farmer's footpath single-tracks and tourist mountain footpaths.

XC bikes are widely available, but you'll need to spend over 3000 RMB for anything really capable, and 1000 for something that is OK, spending less than this will could result in a bike which may be even dangerous as bearing, brake and drive-train quality can be questionable, stick to brands known in the west to be safe.

Freeride and downhill bikes are not that useful unless there are specific places to you them in your area, also with fork and shock servicing still in its infancy in China a hard-tail with strong moderately priced forks is probably a good choice. Although drive-train adjustment and wheel truing can be competently performed.

As far as streets go racing bikes and various types of hybrid bikes are common. BMX bikes usually need to be ordered.